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• 14 December 2023

The most important issue about water is not supply, but how it is used

• Peter Gleick 0

Peter Gleick is co-founder and a senior fellow at the Pacific Institute in Oakland, California. He is the author of The Three Ages of Water: Prehistoric Past, Imperiled Present, and a Hope for the Future (2023)

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Floods, droughts, pollution, water scarcity and conflict — humanity’s relationship with water is deteriorating, and it is threatening our health and well-being, as well as that of the environment that sustains us. The good news is that a transition from the water policies and technologies of past centuries to more effective and equitable ways of using and preserving this vital resource is not only possible, but under way. The challenge is to accelerate and broaden the transition.

Water policies have typically fostered a reliance on centralized, often massive infrastructure, such as big dams for flood and drought protection, and aqueducts and pipelines to move water long distances. Governments have also created narrow institutions focused on water, to the detriment of the interconnected issues of food security, climate, energy and ecosystem health. The key assumption of these ‘hard path’ strategies is that society must find more and more supply to meet what was assumed to be never-ending increases in demand.

Nature Outlook: Water

That focus on supply has brought great benefits to many people, but it has also had unintended and increasingly negative consequences. Among these are the failure to provide safe water and sanitation to all; unsustainable overdraft of ground water to produce the food and fibre that the world’s 8 billion people need; inadequate regulation of water pollutants; massive ecological disruption of aquatic ecosystems; political and violent conflict over water resources; and now, accelerating climate disruption to water systems 1 .

A shift away from the supply-oriented hard path is possible — and necessary. Central to this change will be a transition to a focus on demand, efficiency and reuse, and on protecting and restoring ecosystems harmed by centuries of abuse. Society must move away from thinking about how to take more water from already over-tapped rivers, lakes and aquifers, and instead find ways to do the things we want with less water. These include, water technologies to transform industries and allow people to grow more food; appliances to reduce the amount of water used to flush toilets, and wash clothes and dishes; finding and plugging leaks in water-distribution systems and homes; and collecting, treating and reusing waste water.

Remarkably, and unbeknown to most people, the transition to a more efficient and sustainable future is already under way.

Singapore and Israel, two highly water-stressed regions, use much less water per person than do other high-income countries, and they recycle, treat and reuse more than 80% of their waste water 2 . New technologies, including precision irrigation, real-time soil-moisture monitoring and highly localized weather-forecasting models, allow farmers to boost yields and crop quality while cutting water use. Damaging, costly and dangerous dams are being removed, helping to restore rivers and fisheries.

Source: US Geological Survey

In the United States, total water use is decreasing even though the population and the economy are expanding. Water withdrawals are much less today than they were 50 years ago (see ‘A dip in use’) — evidence that an efficiency revolution is under way. And the United States is indeed doing more with less, because during this time, there has been a marked increase in the economic productivity of water use, measured as units of gross domestic product per unit of water used (see ‘Doing more with less’). Similar trends are evident in many other countries.

Source: US Geological Survey/US Department of Commerce.

Overcoming barriers

The challenge is how to accelerate this transition and overcome barriers to more sustainable and equitable water systems. One important obstacle is the lack of adequate financing and investment in expanding, upgrading and maintaining water systems. Others are institutional resistance in the form of weak or misdirected regulations, antiquated water-rights laws, and inadequate training of water managers with outdated ideas and tools. Another is blind adherence by authorities to old-fashioned ideas or simple ignorance about both the risks of the hard path and the potential of alternatives.

Funding for the modernization of water systems must be increased. In the United States, President Biden’s Infrastructure Investment and Jobs Act provides US$82.5 billion for water-related programmes, including removing toxic lead pipes and providing water services to long-neglected front-line communities. These communities include those dependent on unregulated rural water systems, farm-worker communities in California’s Central Valley, Indigenous populations and those in low-income urban centres with deteriorating infrastructure. That’s a good start. But more public- and private-investments are needed, especially to provide modern water and sanitation systems globally for those who still lack them, and to improve efficiency and reuse.

Regulations have been helpful in setting standards to cut waste and improve water quality, but further standards — and stronger enforcement — are needed to protect against new pollutants. Providing information on how to cut food waste on farms and in food processing, and how to shift diets to less water-intensive food choices can help producers and consumers to reduce their water footprints 3 . Corporations must expand water stewardship efforts in their operations and supply chains. Water institutions must be reformed and integrated with those that deal with energy and climate challenges. And we must return water to the environment to restore ecological systems that, in turn, protect human health and well-being.

In short, the status quo is not acceptable. Efforts must be made at all levels to accelerate the shift from simply supplying more water to meeting human and ecological water needs as carefully and efficiently as possible. No new technologies need to be invented for this to happen, and the economic costs of the transition are much less than the costs of failing to do so. Individuals, communities, corporations and governments all have a part to play. A sustainable water future is possible if we choose the right path.

doi: https://doi.org/10.1038/d41586-023-03899-2

This article is part of Nature Outlook: Water , a supplement produced with financial support from the FII Institute. Nature maintains full independence in all editorial decisions related to the content. About this content .

Caretta, M. A. et al . In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (eds Portner, H.-O. et al .) 551–712 (Cambridge Univ. Press, 2022)

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Giakoumis, T., Vaghela, C. & Voulvoulis, N. Adv. Chem. Pollut. Environ. Manag. Protect. 5 , 227–252 (2020).

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Article Contents

Introduction, physiological effects of dehydration, hydration and chronic diseases, water consumption and requirements and relationships to total energy intake, water requirements: evaluation of the adequacy of water intake, acknowledgments, water, hydration, and health.

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Barry M Popkin, Kristen E D'Anci, Irwin H Rosenberg, Water, hydration, and health, Nutrition Reviews , Volume 68, Issue 8, 1 August 2010, Pages 439–458, https://doi.org/10.1111/j.1753-4887.2010.00304.x

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This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Water is essential for life. From the time that primeval species ventured from the oceans to live on land, a major key to survival has been the prevention of dehydration. The critical adaptations cross an array of species, including man. Without water, humans can survive only for days. Water comprises from 75% body weight in infants to 55% in the elderly and is essential for cellular homeostasis and life. 1 Nevertheless, there are many unanswered questions about this most essential component of our body and our diet. This review attempts to provide some sense of our current knowledge of water, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, the effects of variation in water intake on health and energy intake, weight, and human performance and functioning.

Recent statements on water requirements have been based on retrospective recall of water intake from food and beverages among healthy, noninstitutionalized individuals. Provided here are examples of water intake assessment in populations to clarify the need for experimental studies. Beyond these circumstances of dehydration, it is not fully understood how hydration affects health and well-being, even the impact of water intakes on chronic diseases. Recently, Jéquier and Constant 2 addressed this question based on human physiology, but more knowledge is required about the extent to which water intake might be important for disease prevention and health promotion.

As noted later in the text, few countries have developed water requirements and those that exist are based on weak population-level measures of water intake and urine osmolality. 3 , 4 The European Food Safety Authority (EFSA) was recently asked to revise existing recommended intakes of essential substances with a physiological effect, including water since this nutrient is essential for life and health. 5

The US Dietary Recommendations for water are based on median water intakes with no use of measurements of the dehydration status of the population to assist. One-time collection of blood samples for the analysis of serum osmolality has been used by the National Health and Nutrition Examination Survey program. At the population level, there is no accepted method of assessing hydration status, and one measure some scholars use, hypertonicity, is not even linked with hydration in the same direction for all age groups. 6 Urine indices are used often but these reflect the recent volume of fluid consumed rather than a state of hydration. 7 Many scholars use urine osmolality to measure recent hydration status. 8 , – 12 Deuterium dilution techniques (isotopic dilution with D 2 O, or deuterium oxide) allow measurement of total body water but not water balance status. 13 Currently, there are no completely adequate biomarkers to measure hydration status at the population level.

In discussing water, the focus is first and foremost on all types of water, whether it be soft or hard, spring or well, carbonated or distilled. Furthermore, water is not only consumed directly as a beverage; it is also obtained from food and to a very small extent from oxidation of macronutrients (metabolic water). The proportion of water that comes from beverages and food varies according to the proportion of fruits and vegetables in the diet. The ranges of water content in various foods are presented in Table 1 . In the United States it is estimated that about 22% of water intake comes from food while the percentages are much higher in European countries, particularly a country like Greece with its higher intake of fruits and vegetables, or in South Korea. 3 , – 15 The only in-depth study performed in the United States of water use and water intrinsic to food found a 20.7% contribution from food water; 16 , 17 however, as shown below, this research was dependent on poor overall assessment of water intake.

Ranges of water content for selected foods.

Data from the USDA national nutrient database for standard reference, release 21, as provided in Altman. 126

This review considers water requirements in the context of recent efforts to assess water intake in US populations. The relationship between water and calorie intake is explored both for insights into the possible displacement of calories from sweetened beverages by water and to examine the possibility that water requirements would be better expressed in relation to calorie/energy requirements with the dependence of the latter on age, size, gender, and physical activity level. Current understanding of the exquisitely complex and sensitive system that protects land animals against dehydration is covered and commentary is provided on the complications of acute and chronic dehydration in man, against which a better expression of water requirements might complement the physiological control of thirst. Indeed, the fine intrinsic regulation of hydration and water intake in individuals mitigates prevalent underhydration in populations and its effects on function and disease.

Regulation of fluid intake

To prevent dehydration, reptiles, birds, vertebrates, and all land animals have evolved an exquisitely sensitive network of physiological controls to maintain body water and fluid intake by thirst. Humans may drink for various reasons, particularly for hedonic ones, but drinking is most often due to water deficiency that triggers the so-called regulatory or physiological thirst. The mechanism of thirst is quite well understood today and the reason nonregulatory drinking is often encountered is related to the large capacity of the kidneys to rapidly eliminate excesses of water or to reduce urine secretion to temporarily economize on water. 1 But this excretory process can only postpone the necessity of drinking or of ceasing to drink an excess of water. Nonregulatory drinking is often confusing, particularly in wealthy societies that have highly palatable drinks or fluids that contain other substances the drinker seeks. The most common of these are sweeteners or alcohol for which water is used as a vehicle. Drinking these beverages is not due to excessive thirst or hyperdipsia, as can be shown by offering pure water to individuals instead and finding out that the same drinker is in fact hypodipsic (characterized by abnormally diminished thirst). 1

Fluid balance of the two compartments

Maintaining a constant water and mineral balance requires the coordination of sensitive detectors at different sites in the body linked by neural pathways with integrative centers in the brain that process this information. These centers are also sensitive to humoral factors (neurohormones) produced for the adjustment of diuresis, natriuresis, and blood pressure (angiotensin mineralocorticoids, vasopressin, atrial natriuretic factor). Instructions from the integrative centers to the “executive organs” (kidney, sweat glands, and salivary glands) and to the part of the brain responsible for corrective actions such as drinking are conveyed by certain nerves in addition to the above-mentioned substances. 1

Most of the components of fluid balance are controlled by homeostatic mechanisms responding to the state of body water. These mechanisms are sensitive and precise, and are activated with deficits or excesses of water amounting to only a few hundred milliliters. A water deficit produces an increase in the ionic concentration of the extracellular compartment, which takes water from the intracellular compartment causing cells to shrink. This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys, mainly via the antidiuretic hormone vasopressin to produce a smaller volume of more concentrated urine. 18 When the body contains an excess of water, the reverse processes occur: the lower ionic concentration of body fluids allows more water to reach the intracellular compartment. The cells imbibe, drinking is inhibited, and the kidneys excrete more water.

The kidneys thus play a key role in regulating fluid balance. As discussed later, the kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water and produce more concentrated urine, they expend a greater amount of energy and incur more wear on their tissues. This is especially likely to occur when the kidneys are under stress, e.g., when the diet contains excessive amounts of salt or toxic substances that need to be eliminated. Consequently, drinking a sufficient amount of water helps protect this vital organ.

Regulatory drinking

Most drinking occurs in response to signals of water deficit. Apart from urinary excretion, the other main fluid regulatory process is drinking, which is mediated through the sensation of thirst. There are two distinct mechanisms of physiological thirst: the intracellular and the extracellular mechanisms. When water alone is lost, ionic concentration increases. As a result, the intracellular space yields some of its water to the extracellular compartment. Once again, the resulting shrinkage of cells is detected by brain receptors that send hormonal messages to induce drinking. This association with receptors that govern extracellular volume is accompanied by an enhancement of appetite for salt. Thus, people who have been sweating copiously prefer drinks that are relatively rich in Na+ salts rather than pure water. When excessive sweating is experienced, it is also important to supplement drinks with additional salt.

The brain's decision to start or stop drinking and to choose the appropriate drink is made before the ingested fluid can reach the intra- and extracellular compartments. The taste buds in the mouth send messages to the brain about the nature, and especially the salt content, of the ingested fluid, and neuronal responses are triggered as if the incoming water had already reached the bloodstream. These are the so-called anticipatory reflexes: they cannot be entirely “cephalic reflexes” because they arise from the gut as well as the mouth. 1

The anterior hypothalamus and pre-optic area are equipped with osmoreceptors related to drinking. Neurons in these regions show enhanced firing when the inner milieu gets hyperosmotic. Their firing decreases when water is loaded in the carotid artery that irrigates the neurons. It is remarkable that the same decrease in firing in the same neurons takes place when the water load is applied on the tongue instead of being injected into the carotid artery. This anticipatory drop in firing is due to communication from neural pathways that depart from the mouth and converge onto neurons that simultaneously sense the blood's inner milieu.

Nonregulatory drinking

Although everyone experiences thirst from time to time, it plays little role in the day-to-day control of water intake in healthy people living in temperate climates. In these regions, people generally consume fluids not to quench thirst, but as components of everyday foods (e.g., soup, milk), as beverages used as mild stimulants (tea, coffee), and for pure pleasure. A common example is alcohol consumption, which can increase individual pleasure and stimulate social interaction. Drinks are also consumed for their energy content, as in soft drinks and milk, and are used in warm weather for cooling and in cold weather for warming. Such drinking seems to also be mediated through the taste buds, which communicate with the brain in a kind of “reward system”, the mechanisms of which are just beginning to be understood. This bias in the way human beings rehydrate themselves may be advantageous because it allows water losses to be replaced before thirst-producing dehydration takes place. Unfortunately, this bias also carries some disadvantages. Drinking fluids other than water can contribute to an intake of caloric nutrients in excess of requirements, or in alcohol consumption that, in some people, may insidiously bring about dependence. For example, total fluid intake increased from 79 fluid ounces in 1989 to 100 fluid ounces in 2002 among US adults, with the difference representing intake of caloric beverages. 19

Effects of aging on fluid intake regulation

The thirst and fluid ingestion responses of older persons to a number of stimuli have been compared to those of younger persons. 20 Following water deprivation, older individuals are less thirsty and drink less fluid compared to younger persons. 21 , 22 The decrease in fluid consumption is predominantly due to a decrease in thirst, as the relationship between thirst and fluid intake is the same in young and old persons. Older persons drink insufficient amounts of water following fluid deprivation to replenish their body water deficit. 23 When dehydrated older persons are offered a highly palatable selection of drinks, this also fails to result in increased fluid intake. 23 The effects of increased thirst in response to an osmotic load have yielded variable responses, with one group reporting reduced osmotic thirst in older individuals 24 and one failing to find a difference. In a third study, young individuals ingested almost twice as much fluid as old persons, even though the older subjects had a much higher serum osmolality. 25

Overall, these studies support small changes in the regulation of thirst and fluid intake with aging. Defects in both osmoreceptors and baroreceptors appear to exist as do changes in the central regulatory mechanisms mediated by opioid receptors. 26 Because the elderly have low water reserves, it may be prudent for them to learn to drink regularly when not thirsty and to moderately increase their salt intake when they sweat. Better education on these principles may help prevent sudden hypotension and stroke or abnormal fatigue, which can lead to a vicious circle and eventually hospitalization.

Thermoregulation

Hydration status is critical to the body's process of temperature control. Body water loss through sweat is an important cooling mechanism in hot climates and in periods of physical activity. Sweat production is dependent upon environmental temperature and humidity, activity levels, and type of clothing worn. Water losses via skin (both insensible perspiration and sweating) can range from 0.3 L/h in sedentary conditions to 2.0 L/h in high activity in the heat, and intake requirements range from 2.5 to just over 3 L/day in adults under normal conditions, and can reach 6 L/day with high extremes of heat and activity. 27 , 28 Evaporation of sweat from the body results in cooling of the skin. However, if sweat loss is not compensated for with fluid intake, especially during vigorous physical activity, a hypohydrated state can occur with concomitant increases in core body temperature. Hypohydration from sweating results in a loss of electrolytes, as well as a reduction in plasma volume, and this can lead to increased plasma osmolality. During this state of reduced plasma volume and increased plasma osmolality, sweat output becomes insufficient to offset increases in core temperature. When fluids are given to maintain euhydration, sweating remains an effective compensation for increased core temperatures. With repeated exposure to hot environments, the body adapts to heat stress and cardiac output and stroke volume return to normal, sodium loss is conserved, and the risk for heat-stress-related illness is reduced. 29 Increasing water intake during this process of heat acclimatization will not shorten the time needed to adapt to the heat, but mild dehydration during this time may be of concern and is associated with elevations in cortisol, increased sweating, and electrolyte imbalances. 29

Children and the elderly have differing responses to ambient temperature and different thermoregulatory concerns than healthy adults. Children in warm climates may be more susceptible to heat illness than adults due to their greater surface area to body mass ratio, lower rate of sweating, and slower rate of acclimatization to heat. 30 , 31 Children may respond to hypohydration during activity with a higher relative increase in core temperature than adults, 32 and with a lower propensity to sweat, thus losing some of the benefits of evaporative cooling. However, it has been argued that children can dissipate a greater proportion of body heat via dry heat loss, and the concomitant lack of sweating provides a beneficial means of conserving water under heat stress. 30 Elders, in response to cold stress, show impairments in thermoregulatory vasoconstriction, and body water is shunted from plasma into the interstitial and intracellular compartments. 33 , 34 With respect to heat stress, water lost through sweating decreases the water content of plasma, and the elderly are less able to compensate for increased blood viscosity. 33 Not only do they have a physiological hypodipsia, but this can be exaggerated by central nervous system disease 35 and by dementia. 36 In addition, illness and limitations in daily living activities can further limit fluid intake. When reduced fluid intake is coupled with advancing age, there is a decrease in total body water. Older individuals have impaired renal fluid conservation mechanisms and, as noted above, have impaired responses to heat and cold stress. 33 , 34 All of these factors contribute to an increased risk of hypohydration and dehydration in the elderly.

With regard to physiology, the role of water in health is generally characterized in terms of deviations from an ideal hydrated state, generally in comparison to dehydration. The concept of dehydration encompasses both the process of losing body water and the state of dehydration. Much of the research on water and physical or mental functioning compares a euhydrated state, usually achieved by provision of water sufficient to overcome water loss, to a dehydrated state, which is achieved via withholding of fluids over time and during periods of heat stress or high activity. In general, provision of water is beneficial in individuals with a water deficit, but little research supports the notion that additional water in adequately hydrated individuals confers any benefit.

Physical performance

The role of water and hydration in physical activity, particularly in athletes and in the military, has been of considerable interest and is well-described in the scientific literature. 37 , – 39 During challenging athletic events, it is not uncommon for athletes to lose 6–10% of body weight through sweat, thus leading to dehydration if fluids have not been replenished. However, decrements in the physical performance of athletes have been observed under much lower levels of dehydration, i.e., as little as 2%. 38 Under relatively mild levels of dehydration, individuals engaging in rigorous physical activity will experience decrements in performance related to reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort. 40 , 41 Rehydration can reverse these deficits and reduce the oxidative stress induced by exercise and dehydration. 42 Hypohydration appears to have a more significant impact on high-intensity and endurance activity, such as tennis 43 and long-distance running, 44 than on anaerobic activities, 45 such as weight lifting, or on shorter-duration activities, such as rowing. 46

During exercise, individuals may not hydrate adequately when allowed to drink according to thirst. 32 After periods of physical exertion, voluntary fluid intake may be inadequate to offset fluid deficits. 1 Thus, mild-to-moderate dehydration can persist for some hours after the conclusion of physical activity. Research performed on athletes suggests that, principally at the beginning of the training season, they are at particular risk for dehydration due to lack of acclimatization to weather conditions or suddenly increased activity levels. 47 , 48 A number of studies show that performance in temperate and hot climates is affected to a greater degree than performance in cold temperatures. 41 , – 50 Exercise in hot conditions with inadequate fluid replacement is associated with hyperthermia, reduced stroke volume and cardiac output, decreases in blood pressure, and reduced blood flow to muscle. 51

During exercise, children may be at greater risk for voluntary dehydration. Children may not recognize the need to replace lost fluids, and both children as well as coaches need specific guidelines for fluid intake. 52 Additionally, children may require more time to acclimate to increases in environmental temperature than adults. 30 , 31 Recommendations are for child athletes or children in hot climates to begin athletic activities in a well-hydrated state and to drink fluids over and above the thirst threshold.

Cognitive performance

Water, or its lack (dehydration), can influence cognition. Mild levels of dehydration can produce disruptions in mood and cognitive functioning. This may be of special concern in the very young, very old, those in hot climates, and those engaging in vigorous exercise. Mild dehydration produces alterations in a number of important aspects of cognitive function such as concentration, alertness, and short-term memory in children (10–12 y), 32 young adults (18–25 y), 53 , – 56 and the oldest adults (50–82 y). 57 As with physical functioning, mild-to-moderate levels of dehydration can impair performance on tasks such as short-term memory, perceptual discrimination, arithmetic ability, visuomotor tracking, and psychomotor skills. 53 , – 56 However, mild dehydration does not appear to alter cognitive functioning in a consistent manner. 53 , – 58 In some cases, cognitive performance was not significantly affected in ranges from 2% to 2.6% dehydration. 56 , 58 Comparing across studies, performance on similar cognitive tests was divergent under dehydration conditions. 54 , 56 In studies conducted by Cian et al., 53 , 54 participants were dehydrated to approximately 2.8% either through heat exposure or treadmill exercise. In both studies, performance was impaired on tasks examining visual perception, short-term memory, and psychomotor ability. In a series of studies using exercise in conjunction with water restriction as a means of producing dehydration, D'Anci et al. 56 observed only mild decrements in cognitive performance in healthy young men and women athletes. In these experiments, the only consistent effect of mild dehydration was significant elevations of subjective mood score, including fatigue, confusion, anger, and vigor. Finally, in a study using water deprivation alone over a 24-h period, no significant decreases in cognitive performance were seen with 2.6% dehydration. 58 It is therefore possible that heat stress may play a critical role in the effects of dehydration on cognitive performance.

Reintroduction of fluids under conditions of mild dehydration can reasonably be expected to reverse dehydration-induced cognitive deficits. Few studies have examined how fluid reintroduction may alleviate the negative effects of dehydration on cognitive performance and mood. One study 59 examined how water ingestion affected arousal and cognitive performance in young people following a period of 12-h water restriction. While cognitive performance was not affected by either water restriction or water consumption, water ingestion affected self-reported arousal. Participants reported increased alertness as a function of water intake. Rogers et al. 60 observed a similar increase in alertness following water ingestion in both high- and low-thirst participants. Water ingestion, however, had opposite effects on cognitive performance as a function of thirst. High-thirst participants' performance on a cognitively demanding task improved following water ingestion, but low-thirst participants' performance declined. In summary, hydration status consistently affected self-reported alertness, but effects on cognition were less consistent.

Several recent studies have examined the utility of providing water to school children on attentiveness and cognitive functioning in children. 61 , – 63 In these experiments, children were not fluid restricted prior to cognitive testing, but were allowed to drink as usual. Children were then provided with a drink or no drink 20–45 min before the cognitive test sessions. In the absence of fluid restriction and without physiological measures of hydration status, the children in these studies should not be classified as dehydrated. Subjective measures of thirst were reduced in children given water, 62 and voluntary water intake in children varied from 57 mL to 250 mL. In these studies, as in the studies in adults, the findings were divergent and relatively modest. In the research led by Edmonds et al., 61 , 62 children in the groups given water showed improvements in visual attention. However, effects on visual memory were less consistent, with one study showing no effects of drinking water on a spot-the-difference task in 6–7-year-old children 61 and the other showing a significant improvement in a similar task in 7–9-year-old children. 62 In the research described by Benton and Burgess, 63 memory performance was improved by provision of water but sustained attention was not altered with provision of water in the same children.

Taken together, these studies indicate that low-to-moderate dehydration may alter cognitive performance. Rather than indicating that the effects of hydration or water ingestion on cognition are contradictory, many of the studies differ significantly in methodology and in measurement of cognitive behaviors. These variances in methodology underscore the importance of consistency when examining relatively subtle chances in overall cognitive performance. However, in those studies in which dehydration was induced, most combined heat and exercise; this makes it difficult to disentangle the effects of dehydration on cognitive performance in temperate conditions from the effects of heat and exercise. Additionally, relatively little is known about the mechanism of mild dehydration's effects on mental performance. It has been proposed that mild dehydration acts as a physiological stressor that competes with and draws attention from cognitive processes. 64 However, research on this hypothesis is limited and merits further exploration.

Dehydration and delirium

Dehydration is a risk factor for delirium and for delirium presenting as dementia in the elderly and in the very ill. 65 , – 67 Recent work shows that dehydration is one of several predisposing factors for confusion observed in long-term-care residents 67 ; however, in this study, daily water intake was used as a proxy measure for dehydration rather than other, more direct clinical assessments such as urine or plasma osmolality. Older people have been reported as having reduced thirst and hypodipsia relative to younger people. In addition, fluid intake and maintenance of water balance can be complicated by factors such as disease, dementia, incontinence, renal insufficiency, restricted mobility, and drug side effects. In response to primary dehydration, older people have less thirst sensation and reduced fluid intakes in comparison to younger people. However, in response to heat stress, while older people still display a reduced thirst threshold, they do ingest comparable amounts of fluid to younger people. 20

Gastrointestinal function

Fluids in the diet are generally absorbed in the proximal small intestine, and the absorption rate is determined by the rate of gastric emptying to the small intestine. Therefore, the total volume of fluid consumed will eventually be reflected in water balance, but the rate at which rehydration occurs is dependent upon factors affecting the rate of delivery of fluids to the intestinal mucosa. The gastric emptying rate is generally accelerated by the total volume consumed and slowed by higher energy density and osmolality. 68 In addition to water consumed in food (1 L/day) and beverages (circa 2–3 L/day), digestive secretions account for a far greater portion of water that passes through and is absorbed by the gastrointestinal tract (circa 8 L/day). 69 The majority of this water is absorbed by the small intestine, with a capacity of up to 15 L/day with the colon absorbing some 5 L/day. 69

Constipation, characterized by slow gastrointestinal transit, small, hard stools, and difficulty in passing stool, has a number of causes, including medication use, inadequate fiber intake, poor diet, and illness. 70 Inadequate fluid consumption is touted as a common culprit in constipation, and increasing fluid intake is a frequently recommended treatment. Evidence suggests, however, that increasing fluids is only useful to individuals in a hypohydrated state, and is of little utility in euhydrated individuals. 70 In young children with chronic constipation, increasing daily water intake by 50% did not affect constipation scores. 71 For Japanese women with low fiber intake, concomitant low water intake in the diet is associated with increased prevalence of constipation. 72 In older individuals, low fluid intake is a predictor for increased levels of acute constipation, 73 , 74 with those consuming the least amount of fluid having over twice the frequency of constipation episodes than those consuming the most fluid. In one trial, researchers compared the utility of carbonated mineral water in reducing functional dyspepsia and constipation scores to tap water in individuals with functional dyspepsia. 75 When comparing carbonated mineral water to tap water, participants reported improvements in subjective gastric symptoms, but there were no significant improvements in gastric or intestinal function. The authors indicate it is not possible to determine to what degree the mineral content of the two waters contributed to perceived symptom relief, as the mineral water contained greater levels of magnesium and calcium than the tap water. The available evidence suggests that increased fluid intake should only be indicated in individuals in a hypohydrated state. 69 , 71

Significant water loss can occur through the gastrointestinal tract, and this can be of great concern in the very young. In developing countries, diarrheal diseases are a leading cause of death in children, resulting in approximately 1.5–2.5 million deaths per year. 76 Diarrheal illness results not only in a reduction in body water, but also in potentially lethal electrolyte imbalances. Mortality in such cases can many times be prevented with appropriate oral rehydration therapy, by which simple dilute solutions of salt and sugar in water can replace fluid lost by diarrhea. Many consider application of oral rehydration therapy to be one of the significant public health developments of the last century. 77

Kidney function

As noted above, the kidney is crucial in regulating water balance and blood pressure as well as removing waste from the body. Water metabolism by the kidney can be classified into regulated and obligate. Water regulation is hormonally mediated, with the goal of maintaining a tight range of plasma osmolality (between 275 and 290 mOsm/kg). Increases in plasma osmolality and activation of osmoreceptors (intracellular) and baroreceptors (extracellular) stimulate hypothalamic release of arginine vasopressin (AVP). AVP acts at the kidney to decrease urine volume and promote retention of water, and the urine becomes hypertonic. With decreased plasma osmolality, vasopressin release is inhibited, and the kidney increases hypotonic urinary output.

In addition to regulating fluid balance, the kidneys require water for the filtration of waste from the bloodstream and excretion via urine. Water excretion via the kidney removes solutes from the blood, and a minimum obligate urine volume is required to remove the solute load with a maximum output volume of 1 L/h. 78 This obligate volume is not fixed, but is dependent upon the amount of metabolic solutes to be excreted and levels of AVP. Depending on the need for water conservation, basal urine osmolality ranges from 40 mOsm/kg to a maximum of 1,400 mOsm/kg. 78 The ability to both concentrate and dilute urine decreases with age, with a lower value of 92 mOsm/kg and an upper range falling between 500 and 700 mOsm/kg for individuals over the age of 70 years. 79 , – 81 Under typical conditions, in an average adult, urine volume of 1.5 to 2.0 L/day would be sufficient to clear a solute load of 900 to 1,200 mOsm/day. During water conservation and the presence of AVP, this obligate volume can decrease to 0.75–1.0 L/day and during maximal diuresis up to 20 L/day can be required to remove the same solute load. 78 , – 81 In cases of water loading, if the volume of water ingested cannot be compensated for with urine output, having overloaded the kidney's maximal output rate, an individual can enter a hyponatremic state.

Heart function and hemodynamic response

Blood volume, blood pressure, and heart rate are closely linked. Blood volume is normally tightly regulated by matching water intake and water output, as described in the section on kidney function. In healthy individuals, slight changes in heart rate and vasoconstriction act to balance the effect of normal fluctuations in blood volume on blood pressure. 82 Decreases in blood volume can occur, through blood loss (or blood donation), or loss of body water through sweat, as seen with exercise. Blood volume is distributed differently relative to the position of the heart, whether supine or upright, and moving from one position to the other can lead to increased heart rate, a fall in blood pressure, and, in some cases, syncope. This postural hypotension (or orthostatic hypotension) can be mediated by drinking 300–500 mL of water. 83 , 84 Water intake acutely reduces heart rate and increases blood pressure in both normotensive and hypertensive individuals. 85 These effects of water intake on the pressor effect and heart rate occur within 15–20 min of drinking water and can last for up to 60 min. Water ingestion is also beneficial in preventing vasovagal reaction with syncope in blood donors at high risk for post-donation syncope. 86 The effect of water intake in these situations is thought to be due to effects on the sympathetic nervous system rather than to changes in blood volume. 83 , 84 Interestingly, in rare cases, individuals may experience bradycardia and syncope after swallowing cold liquids. 87 , – 89 While swallow syncope can be seen with substances other than water, swallow syncope further supports the notion that the result of water ingestion in the pressor effect has both a neural component as well as a cardiac component.

Water deprivation and dehydration can lead to the development of headache. 90 Although this observation is largely unexplored in the medical literature, some observational studies indicate that water deprivation, in addition to impairing concentration and increasing irritability, can serve as a trigger for migraine and can also prolong migraine. 91 , 92 In those with water deprivation-induced headache, ingestion of water provided relief from headache in most individuals within 30 min to 3 h. 92 It is proposed that water deprivation-induced headache is the result of intracranial dehydration and total plasma volume. Although provision of water may be useful in relieving dehydration-related headache, the utility of increasing water intake for the prevention of headache is less well documented.

The folk wisdom that drinking water can stave off headaches has been relatively unchallenged, and has more traction in the popular press than in the medical literature. Recently, one study examined increased water intake and headache symptoms in headache patients. 93 In this randomized trial, patients with a history of different types of headache, including migraine and tension headache, were either assigned to a placebo condition (a nondrug tablet) or the increased water condition. In the water condition, participants were instructed to consume an additional volume of 1.5 L water/day on top of what they already consumed in foods and fluids. Water intake did not affect the number of headache episodes, but it was modestly associated with reduction in headache intensity and reduced duration of headache. The data from this study suggest that the utility of water as prophylaxis is limited in headache sufferers, and the ability of water to reduce or prevent headache in the broader population remains unknown.

One of the more pervasive myths regarding water intake is its relation to improvements of the skin or complexion. By improvement, it is generally understood that individuals are seeking to have a more “moisturized” look to the surface skin, or to minimize acne or other skin conditions. Numerous lay sources such as beauty and health magazines as well as postings on the Internet suggest that drinking 8–10 glasses of water a day will “flush toxins from the skin” and “give a glowing complexion” despite a general lack of evidence 94 , 95 to support these proposals. The skin, however, is important for maintaining body water levels and preventing water loss into the environment.

The skin contains approximately 30% water, which contributes to plumpness, elasticity, and resiliency. The overlapping cellular structure of the stratum corneum and lipid content of the skin serves as “waterproofing” for the body. 96 Loss of water through sweat is not indiscriminate across the total surface of the skin, but is carried out by eccrine sweat glands, which are evenly distributed over most of the body surface. 97 Skin dryness is usually associated with exposure to dry air, prolonged contact with hot water and scrubbing with soap (both strip oils from the skin), medical conditions, and medications. While more serious levels of dehydration can be reflected in reduced skin turgor, 98 , 99 with tenting of the skin acting as a flag for dehydration, overt skin turgor in individuals with adequate hydration is not altered. Water intake, particularly in individuals with low initial water intake, can improve skin thickness and density as measured by sonogram, 100 offsets transepidermal water loss, and can improve skin hydration. 101 Adequate skin hydration, however, is not sufficient to prevent wrinkles or other signs of aging, which are related to genetics and to sun and environmental damage. Of more utility to individuals already consuming adequate fluids is the use of topical emollients; these will improve skin barrier function and improve the look and feel of dry skin. 102 , 103

Many chronic diseases have multifactorial origins. In particular, differences in lifestyle and the impact of environment are known to be involved and constitute risk factors that are still being evaluated. Water is quantitatively the most important nutrient. In the past, scientific interest with regard to water metabolism was mainly directed toward the extremes of severe dehydration and water intoxication. There is evidence, however, that mild dehydration may also account for some morbidities. 4 , 104 There is currently no consensus on a “gold standard” for hydration markers, particularly for mild dehydration. As a consequence, the effects of mild dehydration on the development of several disorders and diseases have not been well documented.

There is strong evidence showing that good hydration reduces the risk of urolithiasis (see Table 2 for evidence categories). Less strong evidence links good hydration with reduced incidence of constipation, exercise asthma, hypertonic dehydration in the infant, and hyperglycemia in diabetic ketoacidosis. Good hydration is associated with a reduction in urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct, but all these effects need to be confirmed by clinical trials. For other conditions such as bladder or colon cancer, evidence of a preventive effect of maintaining good hydration is not consistent (see Table 3 ).

Categories of evidence used in evaluating the quality of reports.

Data adapted from Manz. 104

Summary of evidence for association of hydration status with chronic diseases.

Categories of evidence: described in Table 2 .

Water consumption, water requirements, and energy intake are linked in fairly complex ways. This is partially because physical activity and energy expenditures affect the need for water but also because a large shift in beverage consumption over the past century or more has led to consumption of a significant proportion of our energy intake from caloric beverages. Nonregulatory beverage intake, as noted earlier, has assumed a much greater role for individuals. 19 This section reviews current patterns of water intake and then refers to a full meta-analysis of the effects of added water on energy intake. This includes adding water to the diet and water replacement for a range of caloric and diet beverages, including sugar-sweetened beverages, juice, milk, and diet beverages. The third component is a discussion of water requirements and suggestions for considering the use of mL water/kcal energy intake as a metric.

Patterns and trends of water consumption

Measurement of total fluid water consumption in free-living individuals is fairly new in focus. As a result, the state of the science is poorly developed, data are most likely fairly incomplete, and adequate validation of the measurement techniques used is not available. Presented here are varying patterns and trends of water intake for the United States over the past three decades followed by a brief review of the work on water intake in Europe.

There is really no existing information to support an assumption that consumption of water alone or beverages containing water affects hydration differentially. 3 , 105 Some epidemiological data suggest water might have different metabolic effects when consumed alone rather than as a component of caffeinated or flavored or sweetened beverages; however, these data are at best suggestive of an issue deserving further exploration. 106 , 107 As shown below, the research of Ershow et al. indicates that beverages not consisting solely of water do contain less than 100% water.

One study in the United States has attempted to examine all the dietary sources of water. 16 , 17 These data are cited in Table 4 as the Ershow study and were based on National Food Consumption Survey food and fluid intake data from 1977–1978. These data are presented in Table 4 for children aged 2–18 years (Panel A) and for adults aged 19 years and older (Panel B). Ershow et al. 16 , 17 spent a great deal of time working out ways to convert USDA dietary data into water intake, including water absorbed during the cooking process, water in food, and all sources of drinking water.

Beverage pattern trends in the United States for children aged 2–18 years and adults aged 19 years and older, (nationally representative).

Note: The data are age and sex adjusted to 1965.

Values stem from the Ershow calculations. 16

These researchers created a number of categories and used a range of factors measured in other studies to estimate the water categories. The water that is found in food, based on food composition table data, was 393 mL for children. The water that was added as a result of cooking (e.g., rice) was 95 mL. Water consumed as a beverage directly as water was 624 mL. The water found in other fluids, as noted, comprised the remainder of the milliliters, with the highest levels in whole-fat milk and juices (506 mL). There is a small discrepancy between the Ershow data regarding total fluid intake measures for these children and the normal USDA figures. That is because the USDA does not remove milk fats and solids, fiber, and other food constituents found in beverages, particularly juice and milk.

A key point illustrated by these nationally representative US data is the enormous variability between survey waves in the amount of water consumed (see Figure 1 , which highlights the large variation in water intake as measured in these surveys). Although water intake by adults and children increased and decreased at the same time, for reasons that cannot be explained, the variation was greater among children than adults. This is partly because the questions the surveys posed varied over time and there was no detailed probing for water intake, because the focus was on obtaining measures of macro- and micronutrients. Dietary survey methods used in the past have focused on obtaining data on foods and beverages containing nutrient and non-nutritive sweeteners but not on water. Related to this are the huge differences between the the USDA surveys and the National Health and Nutrition Examination Survey (NHANES) performed in 1988–1994 and in 1999 and later. In addition, even the NHANES 1999–2002 and 2003–2006 surveys differ greatly. These differences reflect a shift in the mode of questioning with questions on water intake being included as part of a standard 24-h recall rather than as stand-alone questions. Water intake was not even measured in 1965, and a review of the questionnaires and the data reveals clear differences in the way the questions have been asked and the limitations on probes regarding water intake. Essentially, in the past people were asked how much water they consumed in a day and now they are asked for this information as part of a 24-h recall survey. However, unlike for other caloric and diet beverages, there are limited probes for water alone. The results must thus be viewed as crude approximations of total water intake without any strong research to show if they are over- or underestimated. From several studies of water and two ongoing randomized controlled trials performed by us, it is clear that probes that include consideration of all beverages and include water as a separate item result in the provision of more complete data.

Water consumption trends from USDA and NHANES surveys (mL/day/capita), nationally representative. Note: this includes water from fluids only, excluding water in foods. Sources for 1965, 1977–1978, 1989–1991, and 1994–1998, are USDA. Others are NHANES and 2005–2006 is joint USDA and NHANES.

Water consumption data for Europe are collected far more selectively than even the crude water intake questions from NHANES. A recent report from the European Food Safety Agency provides measures of water consumption from a range of studies in Europe. 4 , – 109 Essentially, what these studies show is that total water intake is lower across Europe than in the United States. As with the US data, none are based on long-term, carefully measured or even repeated 24-h recall measures of water intake from food and beverages. In an unpublished examination of water intake in UK adults in 1986–1987 and in 2001–2002, Popkin and Jebb have found that although intake increased by 226 mL/day over this time period, it was still only 1,787 mL/day in the latter period (unpublished data available from BP); this level is far below the 2,793 mL/day recorded in the United States for 2005–2006 or the earlier US figures for comparably aged adults.

A few studies have been performed in the United States and Europe utilizing 24-h urine and serum osmolality measures to determine total water turnover and hydration status. Results of these studies suggest that US adults consume over 2,100 mL of water per day while adults in Europe consume less than half a liter. 4 , 110 Data on total urine collection would appear to be another useful measure for examining total water intake. Of course, few studies aside from the Donald Study of an adolescent cohort in Germany have collected such data on population levels for large samples. 109

Effects of water consumption on overall energy intake

There is an extensive body of literature that focuses on the impact of sugar-sweetened beverages on weight and the risk of obesity, diabetes, and heart disease; however, the perspective of providing more water and its impact on health has not been examined. The literature on water does not address portion sizes; instead, it focuses mainly on water ad libitum or in selected portions compared with other caloric beverages. A detailed meta-analysis of the effects of water intake alone (i.e., adding additional water) and as a replacement for sugar-sweetened beverages, juice, milk, and diet beverages appears elsewhere. 111

In general, the results of this review suggest that water, when consumed in place of sugar-sweetened beverages, juice, and milk, is linked with reduced energy intake. This finding is mainly derived from clinical feeding studies but also from one very good randomized, controlled school intervention and several other epidemiological and intervention studies. Aside from the issue of portion size, factors such as the timing of beverage and meal intake (i.e., the delay between consumption of the beverage and consumption of the meal) and types of caloric sweeteners remain to be considered. However, when beverages are consumed in normal free-living conditions in which five to eight daily eating occasions are the norm, the delay between beverage and meal consumption may matter less. 112 , – 114

The literature on the water intake of children is extremely limited. However, the excellent German school intervention with water suggests the effects of water on the overall energy intake of children might be comparable to that of adults. 115 In this German study, children were educated on the value of water and provided with special filtered drinking fountains and water bottles in school. The intervention schoolchildren increased their water intake by 1.1 glasses/day ( P  < 0.001) and reduced their risk of overweight by 31% (OR = 0.69, P  = 0.40).

Classically, water data are examined in terms of milliliters (or some other measure of water volume consumed per capita per day by age group). This measure does not link fluid intake and caloric intake. Disassociation of fluid and calorie intake is difficult for clinicians dealing with older persons with reduced caloric intake. This milliliter water measure assumes some mean body size (or surface area) and a mean level of physical activity – both of which are determinants of not only energy expenditure but also water balance. Children are dependent on adults for access to water, and studies suggest that their larger surface area to volume ratio makes them susceptible to changes in skin temperatures linked with ambient temperature shifts. 116 One option utilized by some scholars is to explore food and beverage intake in milliliters per kilocalorie (mL/kcal), as was done in the 1989 US recommended dietary allowances. 4 , 117 This is an option that is interpretable for clinicians and which incorporates, in some sense, body size or surface area and activity. Its disadvantage is that water consumed with caloric beverages affects both the numerator and the denominator; however, an alternative measure that could be independent of this direct effect on body weight and/or total caloric intake is not presently known.

Despite its critical importance in health and nutrition, the array of available research that serves as a basis for determining requirements for water or fluid intake, or even rational recommendations for populations, is limited in comparison with most other nutrients. While this deficit may be partly explained by the highly sensitive set of neurophysiological adaptations and adjustments that occur over a large range of fluid intakes to protect body hydration and osmolarity, this deficit remains a challenge for the nutrition and public health community. The latest official effort at recommending water intake for different subpopulations occurred as part of the efforts to establish Dietary Reference Intakes in 2005, as reported by the Institute of Medicine of the National Academies of Science. 3 As a graphic acknowledgment of the limited database upon which to express estimated average requirements for water for different population groups, the Committee and the Institute of Medicine stated: “While it might appear useful to estimate an average requirement (an EAR) for water, an EAR based on data is not possible.” Given the extreme variability in water needs that are not solely based on differences in metabolism, but also on environmental conditions and activities, there is not a single level of water intake that would assure adequate hydration and optimum health for half of all apparently healthy persons in all environmental conditions. Thus, an adequate intake (AI) level was established in place of an EAR for water.

The AIs for different population groups were set as the median water intakes for populations, as reported in the National Health and Nutrition Examination Surveys; however, the intake levels reported in these surveys varied greatly based on the survey years (e.g., NHANES 1988–1994 versus NHANES 1999–2002) and were also much higher than those found in the USDA surveys (e.g., 1989–1991, 1994–1998, or 2005–2006). If the AI for adults, as expressed in Table 5 , is taken as a recommended intake, the wisdom of converting an AI into a recommended water or fluid intake seems questionable. The first problem is the almost certain inaccuracy of the fluid intake information from the national surveys, even though that problem may also exist for other nutrients. More importantly, from the standpoint of translating an AI into a recommended fluid intake for individuals or populations, is the decision that was made when setting the AI to add an additional roughly 20% of water intake, which is derived from some foods in addition to water and beverages. While this may have been a legitimate effort to use total water intake as a basis for setting the AI, the recommendations that derive from the IOM report would be better directed at recommendations for water and other fluid intake on the assumption that the water content of foods would be a “passive” addition to total water intake. In this case, the observations of the dietary reference intake committee that it is necessary for water intake to meet needs imposed by metabolism and environmental conditions must be extended to consider three added factors, namely body size, gender, and physical activity. Those are the well-studied factors that allow a rather precise measurement and determination of energy intake requirements. It is, therefore, logical that those same factors might underlie recommendations to meet water intake needs in the same populations and individuals. Consideration should also be given to the possibility that water intake needs would best be expressed relative to the calorie requirements, as is done regularly in the clinical setting, and data should be gathered to this end through experimental and population research.

Water requirements expressed in relation to energy recommendations.

AI for total fluids derived from dietary reference intakes for water, potassium, sodium, chloride, and sulphate.

Ratios for water intake based on the AI for water in liters/day calculated using EER for each range of physical activity. EER adapted from the Institute of Medicine Dietary Reference Intakes Macronutrients Report, 2002.

It is important to note that only a few countries include water on their list of nutrients. 118 The European Food Safety Authority is developing a standard for all of Europe. 105 At present, only the United States and Germany provide AI values for water. 3 , 119

Another approach to the estimation of water requirements, beyond the limited usefulness of the AI or estimated mean intake, is to express water intake requirements in relation to energy requirements in mL/kcal. An argument for this approach includes the observation that energy requirements for each age and gender group are strongly evidence-based and supported by extensive research taking into account both body size and activity level, which are crucial determinants of energy expenditure that must be met by dietary energy intake. Such measures of expenditure have used highly accurate methods, such as doubly labeled water; thus, estimated energy requirements have been set based on solid data rather than the compromise inherent in the AIs for water. Those same determinants of energy expenditure and recommended intake are also applicable to water utilization and balance, and this provides an argument for pegging water/fluid intake recommendations to the better-studied energy recommendations. The extent to which water intake and requirements are determined by energy intake and expenditure is understudied, but in the clinical setting it has long been practice to supply 1 mL/kcal administered by tube to patients who are unable to take in food or fluids. Factors such as fever or other drivers of increased metabolism affect both energy expenditure and fluid loss and are thus linked in clinical practice. This concept may well deserve consideration in the setting of population intake goals.

Finally, for decades there has been discussion about expressing nutrient requirements per 1,000 kcal so that a single number would apply reasonably across the spectrum of age groups. This idea, which has never been adopted by the Institute of Medicine and the National Academies of Science, may lend itself to an improved expression of water/fluid intake requirements, which must eventually replace the AIs. Table 5 presents the IOM water requirements and then develops a ratio of mL/kcal based on them. The European Food Safety Agency refers positively to the possibility of expressing water intake recommendations in mL/kcal as a function of energy requirements. 105 Outliers in the adult male categories, which reach ratios as high as 1.5, may well be based on the AI data from the United States, which are above those in the more moderate and likely more accurate European recommendations.

The topic of utilizing mL/kcal to examine water intake and water gaps is explored in Table 6 , which takes the full set of water intake AIs for each age-gender grouping and examines total intake. The data suggest a high level of fluid deficiency. Since a large proportion of fluids in the United States is based on caloric beverages and this proportion has changed markedly over the past 30 years, fluid intake increases both the numerator and the denominator of this mL/kcal relationship. Nevertheless, even using 1 mL/kcal as the AI would leave a gap for all children and adolescents. The NHANES physical activity data were also translated into METS/day to categorize all individuals by physical activity level and thus varying caloric requirements. Use of these measures reveals a fairly large fluid gap, particularly for adult males as well as children ( Table 6 ).

Water intake and water intake gaps based on US Water Adequate Intake Recommendations (based on utilization of water and physical activity data from NHANES 2005–2006).

Note: Recommended water intake for actual activity level is the upper end of the range for moderate and active.

A weighted average for the proportion of individuals in each METS-based activity level.

This review has pointed out a number of issues related to water, hydration, and health. Since water is undoubtedly the most important nutrient and the only one for which an absence will prove lethal within days, understanding of water measurement and water requirements is very important. The effects of water on daily performance and short- and long-term health are quite clear. The existing literature indicates there are few negative effects of water intake while the evidence for positive effects is quite clear.

Little work has been done to measure total fluid intake systematically, and there is no understanding of measurement error and best methods of understanding fluid intake. The most definitive US and European documents on total water requirements are based on these extant intake data. 3 , 105 The absence of validation methods for water consumption intake levels and patterns represents a major gap in knowledge. Even varying the methods of probing in order to collect better water recall data has been little explored.

On the other side of the issue is the need to understand total hydration status. There are presently no acceptable biomarkers of hydration status at the population level, and controversy exists about the current knowledge of hydration status among older Americans. 6 , 120 Thus, while scholars are certainly focused on attempting to create biomarkers for measuring hydration status at the population level, the topic is currently understudied.

As noted, the importance of understanding the role of fluid intake on health has emerged as a topic of increasing interest, partially because of the trend toward rising proportions of fluids being consumed in the form of caloric beverages. The clinical, epidemiological, and intervention literature on the effects of added water on health are covered in a related systematic review. 111 The use of water as a replacement for sugar-sweetened beverages, juice, or whole milk has clear effects in that energy intake is reduced by about 10–13% of total energy intake. However, only a few longer-term systematic interventions have investigated this topic and no randomized, controlled, longer-term trials have been published to date. There is thus very minimal evidence on the effects of just adding water to the diet and of replacing water with diet beverages.

There are many limitations to this review. One certainly is the lack of discussion of potential differences in the metabolic functioning of different types of beverages. 121 Since the literature in this area is sparse, however, there is little basis for delving into it at this point. A discussion of the potential effects of fructose (from all caloric sweeteners when consumed in caloric beverages) on abdominal fat and all of the metabolic conditions directly linked with it (e.g., diabetes) is likewise lacking. 122 , – 125 A further limitation is the lack of detailed review of the array of biomarkers being considered to measure hydration status. Since there is no measurement in the field today that covers more than a very short time period, except for 24-hour total urine collection, such a discussion seems premature.

Some ways to examine water requirements have been suggested in this review as a means to encourage more dialogue on this important topic. Given the significance of water to our health and of caloric beverages to our total energy intake, as well as the potential risks of nutrition-related noncommunicable diseases, understanding both the requirements for water in relation to energy requirements, and the differential effects of water versus other caloric beverages, remain important outstanding issues.

This review has attempted to provide some sense of the importance of water to our health, its role in relationship to the rapidly increasing rates of obesity and other related diseases, and the gaps in present understanding of hydration measurement and requirements. Water is essential to our survival. By highlighting its critical role, it is hoped that the focus on water in human health will sharpen.

The authors wish to thank Ms. Frances L. Dancy for administrative assistance, Mr. Tom Swasey for graphics support, Dr. Melissa Daniels for assistance, and Florence Constant (Nestle's Water Research) for advice and references.

This work was supported by the Nestlé Waters, Issy-les-Moulineaux, France, 5ROI AGI0436 from the National Institute on Aging Physical Frailty Program, and NIH R01-CA109831 and R01-CA121152.

Declaration of interest

The authors have no relevant interests to declare.

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• dehydration
• energy intake
• water drinking
• fluid intake
• water requirements

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There are many options for what to drink , but water is the best choice for most people who have access to safe drinking water. It is calorie-free and as easy to find as the nearest tap.

Water helps to restore fluids lost through metabolism, breathing, sweating, and the removal of waste. It helps to keep you from overheating, lubricates the joints and tissues, maintains healthy skin, and is necessary for proper digestion. It’s the perfect zero-calorie beverage for quenching thirst and rehydrating your body.

How Much Water Do I Need?

Water is an essential nutrient at every age, so optimal hydration is a key component for good health. Water accounts for about 60% of an adult’s body weight. We drink fluids when we feel thirst, the major signal alerting us when our body runs low on water. We also customarily drink beverages with meals to help with digestion. But sometimes we drink not based on these factors but on how much we think we should be drinking. One of the most familiar sayings is to aim for “8 glasses a day,” but this may not be appropriate for every person.

General recommendations

• The National Academy of Medicine suggests an adequate intake of daily fluids of about 13 cups and 9 cups for healthy men and women, respectively, with 1 cup equaling 8 ounces. [1] Higher amounts may be needed for those who are physically active or exposed to very warm climates. Lower amounts may be needed for those with smaller body sizes. It’s important to note that this amount is not a daily target, but a general guide. In the average person, drinking less will not necessarily compromise one’s health as each person’s exact fluid needs vary, even day-to-day.
• Fever, exercise, exposure to extreme temperature climates (very hot or cold), and excessive loss of body fluids (such as with vomiting or diarrhea) will increase fluid needs.
• The amount and color of urine can provide a rough estimate of adequate hydration. Generally the color of urine darkens the more concentrated it is (meaning that it contains less water). However, foods, medications, and vitamin supplements can also change urine color. [1] Smaller volumes of urine may indicate dehydration, especially if also darker in color.
• Alcohol can suppress anti-diuretic hormone, a fluid-regulating hormone that signals the kidneys to reduce urination and reabsorb water back into the body. Without it, the body flushes out water more easily. Enjoying more than a couple of drinks within a short time can increase the risk of dehydration, especially if taken on an empty stomach. To prevent this, take alcohol with food and sips of water.
• Although caffeine has long been thought to have a diuretic effect, potentially leading to dehydration, research does not fully support this. The data suggest that more than 180 mg of caffeine daily (about two cups of brewed coffee) may increase urination in the short-term in some people, but will not necessarily lead to dehydration. Therefore, caffeinated beverages including coffee and tea can contribute to total daily water intake. [1]

Keep in mind that about 20% of our total water intake comes not from beverages but from water-rich foods like lettuce, leafy greens, cucumbers, bell peppers, summer squash, celery, berries, and melons.

Aside from including water-rich foods, the following chart is a guide for daily water intake based on age group from the National Academy of Medicine:

Preventing Dehydration: Is Thirst Enough?

As we age, however, the body’s regulation of fluid intake and thirst decline. Research has shown that both of these factors are impaired in the elderly. A Cochrane review found that commonly used indicators of dehydration in older adults (e.g., urine color and volume, feeling thirsty) are not effective and should not be solely used. [3] Certain conditions that impair mental ability and cognition, such as a stroke or dementia, can also impair thirst. People may also voluntarily limit drinking due to incontinence or difficulty getting to a bathroom. In addition to these situations, research has found that athletes, people who are ill, and infants may not have an adequate sense of thirst to replete their fluid needs. [2] Even mild dehydration may produce negative symptoms, so people who cannot rely on thirst or other usual measures may wish to use other strategies. For example, aim to fill a 20-ounce water bottle four times daily and sip throughout the day, or drink a large glass of water with each meal and snack.

Symptoms of dehydration that may occur with as little as a 2% water deficit:

• Confusion or short-term memory loss
• Mood changes like increased irritability or depression

Dehydration can increase the risk of certain medical conditions:

• Urinary tract infections
• Kidney stones
• Constipation  

Like most trends of the moment, alkaline water has become popular through celebrity backing with claims ranging from weight loss to curing cancer. The theory behind alkaline water is the same as that touting the benefits of eating alkaline foods, which purportedly counterbalances the health detriments caused by eating acid-producing foods like meat, sugar, and some grains.

From a scale of 0-14, a higher pH number is alkaline; a lower pH is acidic. The body tightly regulates blood pH levels to about 7.4 because veering away from this number to either extreme can cause negative side effects and even be life-threatening. However, diet alone cannot cause these extremes; they most commonly occur with conditions like uncontrolled diabetes, kidney disease, chronic lung disease, or alcohol abuse.

Alkaline water has a higher pH of about 8-9 than tap water of about 7, due to a higher mineral or salt content. Some water sources can be naturally alkaline if the water picks up minerals as it passes over rocks. However, most commercial brands of alkaline water have been manufactured using an ionizer that reportedly separates out the alkaline components and filters out the acid components, raising the pH. Some people add an alkaline substance like baking soda to regular water.

Scientific evidence is not conclusive on the acid-alkaline theory, also called the acid-ash theory, stating that eating a high amount of certain foods can slightly lower the pH of blood especially in the absence of eating foods supporting a higher alkaline blood pH like fruits, vegetables, and legumes. Controlled clinical trials have not shown that diet alone can significantly change the blood pH of healthy people. Moreover, a direct connection of blood pH in the low-normal range and chronic disease in humans has not been established.

BOTTOM LINE: If the idea of alkaline water encourages you to drink more, then go for it! But it’s likely that drinking plain regular water will provide similar health benefits from simply being well-hydrated—improved energy, mood, and digestive health

Is It Possible To Drink Too Much Water?

There is no Tolerable Upper Intake Level for water because the body can usually excrete extra water through urine or sweat. However, a condition called water toxicity is possible in rare cases, in which a large amount of fluids is taken in a short amount of time, which is faster than the kidney’s ability to excrete it. This leads to a dangerous condition called hyponatremia in which blood levels of sodium fall too low as too much water is taken. The excess total body water dilutes blood sodium levels, which can cause symptoms like confusion, nausea, seizures, and muscle spasms. Hyponatremia is usually only seen in ill people whose kidneys are not functioning properly or under conditions of extreme heat stress or prolonged strenuous exercise where the body cannot excrete the extra water. Very physically active people such as triathletes and marathon runners are at risk for this condition as they tend to drink large amounts of water, while simultaneously losing sodium through their sweat. Women and children are also more susceptible to hyponatremia because of their smaller body size.

Fun Flavors For Water  

Infused water

Instead of purchasing expensive flavored waters in the grocery store, you can easily make your own at home. Try adding any of the following to a cold glass or pitcher of water:

• Sliced citrus fruits or zest (lemon, lime, orange, grapefruit)
• Crushed fresh mint
• Peeled, sliced fresh ginger or sliced cucumber
• Crushed berries

Sparkling water with a splash of juice

Sparkling juices may have as many calories as sugary soda. Instead, make your own sparkling juice at home with 12 ounces of sparkling water and just an ounce or two of juice. For additional flavor, add sliced citrus or fresh herbs like mint.

TIP: To reduce waste, reconsider relying on single-use plastic water bottles and purchase a colorful 20-32 ounce refillable water thermos that is easy to wash and tote with you during the day. 

Are seltzers and other fizzy waters safe and healthy to drink?

BOTTOM LINE: Carbonated waters, if unsweetened, are safe to drink and a good beverage choice. They are not associated with health problems that are linked with sweetened, carbonated beverages like soda.

• Harvard T.H. Chan School of Public Health is a member of the Nutrition and Obesity Policy Research and Evaluation Network’s (NOPREN) Drinking Water Working Group. A collaborative network of the Centers for Disease Control and Prevention, the NOPREN Drinking Water Working Group focuses on policies and economic issues regarding free and safe drinking water access in various settings by conducting research and evaluation to help identify, develop and implement drinking-water-related policies, programs, and practices. Visit the network’s website to access recent water research and evidence-based resources.
• The Harvard Prevention Research Center on Nutrition and Physical Activity provides tools and resources for making clean, cold, free water more accessible in environments like schools and afterschool programs, as well as tips for making water more tasty and fun for kids.
• The National Academy of Sciences. Dietary References Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. https://www.nap.edu/read/10925/chapter/6#102 Accessed 8/5/2019.
• Millard-Stafford M, Wendland DM, O’Dea NK, Norman TL. Thirst and hydration status in everyday life. Nutr Rev . 2012 Nov;70 Suppl 2:S147-51.
• Hooper L, Abdelhamid A, Attreed NJ, Campbell WW, Channell AM, et al. Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people. Cochrane Database Syst Rev . 2015 Apr 30;(4):CD009647.

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• Research article
• Open access
• Published: 17 July 2020

The quality of drinking and domestic water from the surface water sources (lakes, rivers, irrigation canals and ponds) and springs in cholera prone communities of Uganda: an analysis of vital physicochemical parameters

• Godfrey Bwire   ORCID: orcid.org/0000-0002-8376-2857 1 ,
• David A. Sack 2 ,
• Atek Kagirita 3 ,
• Tonny Obala 4 ,
• Amanda K. Debes 2 ,
• Malathi Ram 2 ,
• Henry Komakech 1 ,
• Christine Marie George 2 &
• Christopher Garimoi Orach 1  

BMC Public Health volume  20 , Article number:  1128 ( 2020 ) Cite this article

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Water is the most abundant resource on earth, however water scarcity affects more than 40% of people worldwide. Access to safe drinking water is a basic human right and is a United Nations Sustainable Development Goal (SDG) 6. Globally, waterborne diseases such as cholera are responsible for over two million deaths annually. Cholera is a major cause of ill-health in Africa and Uganda. This study aimed to determine the physicochemical characteristics of the surface and spring water in cholera endemic communities of Uganda in order to promote access to safe drinking water.

A longitudinal study was carried out between February 2015 and January 2016 in cholera prone communities of Uganda. Surface and spring water used for domestic purposes including drinking from 27 sites (lakes, rivers, irrigation canal, springs and ponds) were tested monthly to determine the vital physicochemical parameters, namely pH, temperature, dissolved oxygen, conductivity and turbidity.

Overall, 318 water samples were tested. Twenty-six percent (36/135) of the tested samples had mean test results that were outside the World Health Organization (WHO) recommended drinking water range. All sites (100%, 27/27) had mean water turbidity values greater than the WHO drinking water recommended standards and the temperature of above 17 °C. In addition, 27% (3/11) of the lake sites and 2/5 of the ponds had pH and dissolved oxygen respectively outside the WHO recommended range of 6.5–8.5 for pH and less than 5 mg/L for dissolved oxygen. These physicochemical conditions were ideal for survival of Vibrio. cholerae .

Conclusions

This study showed that surface water and springs in the study area were unsafe for drinking and had favourable physicochemical parameters for propagation of waterborne diseases including cholera. Therefore, for Uganda to attain the SDG 6 targets and to eliminate cholera by 2030, more efforts are needed to promote access to safe drinking water. Also, since this study only established the vital water physicochemical parameters, further studies are recommended to determine the other water physicochemical parameters such as the nitrates and copper. Studies are also needed to establish the causal-effect relationship between V. cholerae and the physicochemical parameters.

Peer Review reports

Water is the most abundant resource on the planet earth [ 1 ], however its scarcity affects more than 40% of the people around the world [ 2 ]. Natural water is an important material for the life of both animals and plants on the earth [ 3 ]. Consequently, access to safe drinking water is essential for health and a basic human right that is integral to the United Nations Resolution 64/292 of 2010 [ 4 ]. The United Nations set 2030 as the timeline for all countries and people to have universal access to safe drinking water; this is a Sustainable Development Goal (SDG) 6 of the 17 SDGs [ 5 ]. The availability of and access to safe water is more important to existence in Africa than it is elsewhere in the world [ 6 ]. Least Developed Countries (LDCs) especially in sub-Saharan Africa have the lowest access to safe drinking water [ 7 ]. In Africa, rural residents have far less access to safe drinking water and sanitation than their urban counterparts [ 8 ].

Natural water exists in three forms namely; ground water, rain water and surface water. Of the three forms, surface water is the most accessible. Worldwide, 144 million people depend on surface water for their survival [ 9 ]. In Uganda, 7% of the population depends on surface water (lakes, rivers, irrigation canal, ponds) for drinking water [ 10 ]. The same surface water is a natural habitat for many living organisms [ 11 ] some of which are responsible for transmission of infectious diseases such as cholera, typhoid, dysentery, guinea worm among others [ 12 ]. Surface water sources include lakes, rivers, streams, canals, and ponds. These surface water sources are often vulnerable to contamination by human, animal activities and weather (storms or heavy rain) [ 13 , 14 ]. Globally, waterborne diseases such as diarrheal are responsible for more than two million deaths annually. The majority of these deaths occur among children under-5 years of age [ 15 ].

Cholera, a waterborne disease causes many deaths each year in Africa, Asia and Latin America [ 16 ]. In 2018 alone, a total of 120,652 cholera cases and 2436 deaths were reported from 17 African countries to World Health Organization [ 17 ]. Cholera is a major cause of morbidity and mortality in Uganda [ 18 ]. The fishing communities located along the major lakes and the rivers in the African Great Lakes basin of Uganda constitutes 5% of the Uganda’s population, however these communities were responsible for the majority (58%) of the reported cholera cases during the period 2011–2015 [ 19 ]. Cholera outbreaks affect predominantly communities using the surface water and the springs. There is also high risk of waterborne disease outbreaks in the communities using these types of water [ 20 , 21 ]. Studies of the surface water from water sources located in the lake basins of the five African Great Lakes in Uganda identified Vibrio. cholerae [ 22 , 23 ] though no study isolated the toxigenic V. cholerae O1 or O139 that cause epidemic cholera. Cholera outbreaks in the African Great Lakes basins in Uganda have been shown to be propagated through water contaminated with sewage [ 20 , 24 ]. Cholera is one of the diseases targeted for elimination globally by the WHO by 2030 [ 25 ]. Hence, to prevent and control cholera outbreaks in these communities, promotion of use of safe water (both quantity and quality), improved sanitation and hygiene are the interventions prioritized by the Uganda Ministry of Health [ 26 ]. Most importantly, provision of adequate safe water is a major pillar of an effective cholera prevention program given that water is the main mode of V. cholerae transmission [ 27 , 28 ].

Availability of adequate safe water is essential for prevention of enteric diseases including cholera [ 29 ]. Therefore, access to safe drinking and domestic water in terms of quantity and quality is key to cholera prevention. Water quality is defined in terms of three key quality parameters namely, physical, chemical and microbiological characteristics [ 30 ]. A less common but important parameter is the radiological characteristics [ 31 ]. In regards to the physicochemical parameters, there are five parameters that are essential and impacts life (both flora and or fauna) within the aquatic systems [ 32 ]. These vital physicochemical parameters include pH, temperature, dissolved oxygen, conductivity and turbidity [ 32 ].

pH is a value that is based on logarithm scale of 0–14 [ 33 ]. Aquatic organisms prefer pH range of 6.5–8.5 [ 34 , 35 , 36 ]. Low pH can cause the release of toxic elements or compounds into the water [ 37 ]. The optimal pH for V. cholerae survival is in basic range (above 7). Vibrio cholerae may not survive for long in acidic pH [ 38 ]. A solution of pH below 4.5 will kill V.cholerae bacteria [ 39 ].

Most aquatic organisms are adapted to live in a narrow temperature range and they die when the temperature is too low or too high [ 34 ]. Vibrio cholerae , bacteria proliferate during algae bloom resulting in cholera outbreaks [ 40 , 41 ]. This proliferation could be due favourable warm temperature [ 42 ]. Relatedly, V. cholerae isolation from natural water in endemic settings is strongly correlated with water temperature above 17 °C [ 43 ].

Dissolved oxygen is the oxygen present in water that is available to aquatic organisms [ 34 ]. Dissolved oxygen is measured in parts per million (ppm) or milligrams per litre (mg/L) [ 35 ]. Organisms in water need oxygen in order to survive [ 44 ]. Decomposition of organic materials and sewage are major causes of low dissolved oxygen in water [ 12 ].

Water conductivity is the ability of water to pass an electrical current and is expressed as millisiemens per metre (1 mS m- 1  = 10 μS cm − 1 ) [ 29 ]. Most aquatic organisms can only tolerate a specific conductivity range [ 45 ]. Water conductivity increases with raising temperature [ 46 ]. There is no set standard for water conductivity [ 45 ]. Freshwater sources have conductivity of 100 – 2000μS cm − 1 . High water conductivity may be due to inorganic dissolved solids [ 46 ].

Turbidity is an optical determination of water clarity [ 47 ]. Turbidity can come from suspended sediment such as silt or clay [ 48 ]. High levels of total suspended solids will increase water temperatures and decrease dissolved oxygen (DO) levels [ 12 ]. In addition, some pathogens like V. cholerae, Giardia lambdia and Cryptosporidia exploit the high water turbidity to hide from the effect of water treatment agents and cause waterborne diseases [ 49 ]. Consequently, high water turbidity can promotes the development of harmful algal blooms [ 41 , 50 ].

Given the importance of the water physicochemical parameters, in order to ensure that they are within the acceptable limits, the WHO recommends that they are monitored regularly [ 51 ]. The recommended physicochemical parameters range for raw water are for pH of 6.5–8.5, turbidity of less than 5Nephlometric Units (NTU) and dissolved oxygen of not less than 5 mg/L [ 51 ]. Surface and spring water with turbidity that exceeds 5NTU should be treated to remove suspended matter before disinfection by either sedimentation (coagulation and flocculation) and or filtration [ 52 ].

Water chlorination using chlorine tablets or other chlorine releasing reagent is one of the most common methods employed to disinfect drinking water [ 53 , 54 ]. Chlorination is an important component of cholera prevention and control program [ 55 ]. In addition to disinfection to kill the pathogens, drinking water should also be safe in terms of physicochemical parameters as recommended by WHO [ 51 ]. However, to effectively make the water safe using chlorine tablets and other reagents, knowledge of the physicochemical properties of the surface and spring water being disinfected is important as several of the parameters affect the active component in the chlorine tablets [ 56 ]. For example, chlorine is not effective for water with pH above 8.5 or turbidity of above 5NTU [ 53 ].

Generally, there is scarcity of information about the quality and safety of drinking water in Africa [ 57 ]. Similarly, few studies exist on the physicochemical characteristics of the drinking water and water in general in Uganda. Furthermore, information from such studies is inadequate for use to increase safe water in cholera prone districts of Uganda where the need is greatest. The cholera endemic communities of Uganda [ 19 , 21 , 24 ] have adequate quantities of water that is often collected from the Great lakes, rivers and other surface water sources located within the lake basins. However, the water is of poor quality in terms of physicochemical and microbiological characteristics. Several studies conducted in Uganda have documented microbiological contamination of drinking water [ 20 , 24 , 58 , 59 ]. However, few studies exist on the physicochemical characteristics of these water. Furthermore, these studies focused on few water sources, for example testing the lakes and omitted the rivers, springs and ponds or testing the rivers and omitted the other water types. One such study was carried out on the water from the three lakes in western Rift valley and Lake Victoria in Uganda [ 23 ], This study did not assess the other common water sources such as the rivers, ponds and springs that were used by the communities for drinking and other household purposes. Other studies on water physicochemical characteristics assessed heavy metal water pollution of River Rwizi (Mbarara district, Western Uganda) [ 60 ] and of the drinking water (bottled, ground and tap water) in Kampala City (Central Uganda) [ 61 ] and Bushenyi district (Western Uganda) [ 62 ]. These studies found high heavy metal water pollution in the drinking water tested. The information gathered from such studies is useful in specific study area and is inadequate to address the lack of safe water in the cholera endemic districts of Uganda where the need for safe drinking water is greatest. Several epidemiological studies in Uganda have attributed cholera outbreaks to use of contaminated surface water [ 20 , 21 , 24 , 63 ]. Furthermore, studies conducted on the surface water focus on pathogen identification [ 63 , 64 ] leaving out the water physicochemical parameters which are equally important in the provision of safe drinking water [ 53 ] and are necessary for survival of all living organisms (both animals and plants) [ 44 ].

Therefore, the aim of this study was to determine the physicochemical characteristics of the surface water sources and springs located in African Great Lakes basins in Uganda so as to guide the interventions for provision of safe water to cholera prone populations [ 19 , 20 , 21 , 24 , 58 ] of Uganda. This study in addition has the potential to guide Uganda to attain the United Nations SDG 6 target of universal access to safe drinking water [ 2 ] and the WHO cholera elimination Roadmap [ 25 ] by 2030. Furthermore, these findings may guide future studies including those on causal-effect relationship between physicochemical parameters and infectious agents (pathogens).

This was a longitudinal study that was conducted between February 2015 and January 2016 in six districts of Uganda that are located in the African Great Lakes basins of the five lakes (Victoria, Albert, Kyoga, Edward and George). These districts had ongoing cholera outbreaks or history of cholera outbreaks in the previous five to 10 years (2005–2015). In addition, the selected study districts had border access to the following major water bodies (lakes: Victoria, Albert, Edward, George and Kyoga). The study area was purposively selected because the communities residing along these major lakes contributed most (58%) of the reported cholera cases and deaths in Uganda [ 19 , 65 ] and in the sub-Saharan Africa region [ 66 ] in the past 10 years. Water samples were collected monthly from 27 sites used by the communities for household purposes that included drinking. Water samples were then tested to determine the vital physicochemical parameters. The water samples were collected from lakes, rivers, springs, ponds and an irrigation canal that were located in the lake basins of the five African Great Lakes in Uganda. In one site, water was also collected from a nearby drainage channel and tested for V. cholerae [ 22 ] and physicochemical parameters. However, because the channel was not used for drinking the results were omitted in this article. Water samples were analysed to determine the pH, temperature, dissolve oxygen, conductivity and turbidity. The study sites were located in the districts of Kampala and Kayunga in central region of Uganda; Kasese and Buliisa districts in western Uganda; Nebbi and Busia districts in northern and eastern Uganda respectively. The study sites were the same as for the simultaneous bacteriological V. cholerae detection study [ 22 ] and are shown in Fig.  1 .

Map showing the location of Uganda, the study districts, major surface water sources and the study sites, February 2015 – January 2016. The blue shades are the African Great Lakes and their basins. (Map generated by ArcGIS version 10.2 [licenced] and assembled using Microsoft Office PowerPoint, Version 2016 [licenced] by the authors)

Rural-urban categorization of the study sites

The study sites were categorized as urban if they were found in Kampala district (the Capital City of Uganda) or rural if they were in the other five remote study districts (Kasese, Kayunga, Busia, Nebbi and Buliisa).

Identification of the study sites and water testing procedures

The sites for water testing were identified with the guidance of the local communities and after direct observation by the study team. Geo-coordinates of the sites were taken at the beginning of the study to ensure that subsequent water collection and measurements were done on water from specific points. Two water collection sites were selected on each of the African Great Lakes in Uganda. The selected sites were in different locations but within the communities with a history of cholera outbreaks in the previous 10 years prior to the study period. For each selected lake point, a site was also selected on a river, a spring and a pond located within the area and being used by the communities for domestic purposes that included drinking and preparation of food. A total of 27 sites, two of which were from each of the five lakes were selected and the water tested. The number of sites on each lake and their locations are shown in Additional file  1 .

Water samples were collected and tested monthly for 12 months by the research assistants who were health workers with background training in microbiology or environmental health. The research assistants received training on water collection and testing from a water engineer. The physicochemical parameters were measured by use of the digital meters namely the Hach meter HQ40d and digital turbidity meter.

Water samples were collected in five-litre containers, three litres were processed for V. cholerae detection by Polymerase Chain Reaction (PCR) test as previously described [ 67 ]. Vibrio cholerae Non O1/Non O139 pathogens were frequently detected in the water samples during the study period [ 22 ]. While the three litres of water were being processed for V. cholerae detection [ 22 ], the rest of the water (2 l), were simultaneously used for the onsite measurement of temperature, pH, conductivity and dissolved oxygen. The Hach meters , HQ40d used in the study, had three electrodes that were calibrated before each monthly testing according to the manufacturers’ manual [ 68 ]. The Hach meter calibrations were done using three specific standard buffer solutions that were for pH, dissolved oxygen and conductivity respectively. Turbidity (total suspended solids or water clarity) was measured using a turbidity meter according to previously published methods [ 49 ]. In addition, the research assistants were provided with Standard Operating Procedures (SOPs) and supervised monthly by the investigators before and during each scheduled monthly measurements.

Data management, analysis and statistical tests

Data were collected, entered, cleaned and stored in the spreadsheet. Errors in the recorded readings were removed using the correct records retrieved from the Hach meters’ HQ40d internal memory. Stata statistical package version 13 was used to analyse the data. Data were analysed to generate means and standard error of the mean for pH, temperature, dissolved oxygen (DO), conductivity (CD) and turbidity. Data were presented in the form of tables and graphs. Comparison for variations between the water samples were carried out using One-Way Analysis of Variance (ANOVA) test. Samples with significant One-Way ANOVA test were subjected to Turkey’s Post Hoc test to establish which of the variables were statistically significant.

The map was created using ArcGIS software, Version 10.2, licenced (ESRI, Redlands, California, USA). The graphs and figures were produced using Microsoft Excel and PowerPoints, Version 2016 (Microsoft, Redmond, Washington, USA). The administrative shapefiles used to create the map were obtained from open access domain, the Humanitarian Data Exchange: https://data.humdata.org/ . In order to generate the study locations on the map, Global Positioning System (GPS) coordinates for the study sites were converted to shapefiles that were combined with the administrative shapefiles corresponding to the locations.

A total of 318 water samples were tested from 27 sites as follows; lake water 40.9%, (130/318), rivers water 26.4% (84/318), ponds water 17.9% (57/318), spring water 11.0% (35/318) and canal water 3.8% (12/318).

Test results for the lake water collected at the fish landing sites (FLS)

The mean physicochemical test results for pH, temperature, dissolved oxygen, conductivity and turbidity are shown in Table  1 .

The mean physicochemical water characteristics of most of the sites were within the WHO recommended water safety range except for turbidity. Few sites had pH and dissolved oxygen outside the WHO recommended safety range.

Monthly variations of the lake water physicochemical characteristics

There were monthly variations in the physicochemical parameters between the water from the lake sites overtime. Most of the sites had steady pH overtime for the first half of the study period (February – August 2015). Thereafter, the pH reduced slightly during the second half (September, 2015 – January, 2016) of the study period. The highest pH fluctuations were in the months of October – December, 2015. The widest change in pH within the same site was observed at Gaaba Fish landing site, Lake Victoria basin, Kampala district.

There were differences in water temperature on the same lake but at different test sites. These differences were detectable mostly in the months of April, 2015. The lowest and highest water temperatures were both recorded on Lake Edward (Kasese district) at Kayanzi fish landing site of 18.9 °C and at Katwe FLS of 34  ° C in the period between April – August, 2015. Fluctuations in the dissolved oxygen were detectable throughout the study period. Kalolo Fish landing site on Lake Albert, Buliisa district showed the widest fluctuations in dissolved oxygen with the highest value of 10.73 mg/L and the lowest of 2.5 mg/L.

Most test sites had small conductivity fluctuations except for Panyimur and Kalolo both of which were located on Lake Albert in Nebbi and Buliisa districts These districts had high water conductivity fluctuations with arrange of 267.1 μS/cm – 2640 μS/cm at Kalolo (Buliisa district) FLS and 296 μS/cm – 2061 μS/cm at Panyimur (Nebbi district). Water turbidity for the majority of the sites changed overtime. Kahendero fish landing site (Lake George, Kasese district) had the highest turbidity which was most noticeable in the months of October 2015 to January 2016. Majanji fish landing site (Lake Victoria, Busia district) had the lowest and most stable water turbidity. Monthly variations of the lake water physicochemical parameters are shown in Fig.  2 .

Monthly variations of lake water physicochemical characteristics (pH, temperature, dissolved oxygen, conductivity and turbidity), February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) water dissolved oxygen; Part d ) water conductivity variations; Part e ) water turbidity variations

River water physicochemical parameter test results

The mean physicochemical characteristics of water from the seven rivers studied are shown in Table  2 .

There were variations in the mean pH, temperature, dissolved oxygen and conductivity between study sites on the rivers. However, these mean parameter variations were in WHO acceptable drinking water safety limit except for River Lubigi, Kampala district which had mean dissolved oxygen below the recommended WHO range. At one time (February, 2015) River Lubigi had dissolved oxygen of 0.45 mg/L. The river water turbidity for all the test sites were above that recommended by WHO of less than 5NTU.

Monthly variations of the river water physicochemical characteristics

Monthly variations in the water physicochemical characteristics of the seven river test sites are shown in Fig.  3 .

Monthly variations of the physicochemical characteristics of river water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) water dissolved oxygen variations; Part d ) water conductivity variations; Part e ) water turbidity variations

There were variations in the water physicochemical parameters between rivers and within the same river overtime. Most rivers showed fluctuations of water pH and temperature. Some rivers such as R. Nyamugasani and R. Lhubiriha both in Kasese district had wide temperature fluctuations. River Mobuku (Kasese district) had the lowest water temperature recorded over the study period. Fluctuations in dissolved oxygen were highest in R. Lubigi (Kampala district), Lake Victoria basin. Dissolved oxygen for R. Lubigi was below the recommended level of more than 5 mg/L for most of the study period. Seasonal variations of water dissolved oxygen were also more noticeable in R. Lubigi than the rest of the river sites. Relatively more dissolved oxygen was found during the rainy seasons (March – July, 2015, first rainy season and September – December, 2015, second rainy season) than in dry season.

There were small variations in the water conductivity in the majority of the rivers. Wide fluctuations in conductivity were observed for water samples of R, Lubigi (Kampala district). River Nyamugasani (Kasese district, Lake Edward basin) had steady but higher conductivity than all the other rivers. There were variations in turbidity within the same river overtime and between the different rivers. River Sio (Busia district) had the highest and the widest turbidity variations during the study period.

Water test results for the springs and ponds

The mean physicochemical characteristics of spring and pond water are shown in Table  3 .

The mean physicochemical characteristics of water from the springs and ponds showed variations between the sites. The majority of site means values were within the WHO accepted pH range. Two sites, Wanseko pond (Buliisa, district, Lake Albert basin) and Katanga spring (Kampala district, Lake Victoria basin) had mean water pH below the recommended WHO drinking water acceptable range at the acidic level of 5.73 and 6.19 respectively. Forty percent (40%, 2/5) of the ponds and 33% (1/3) of the springs had mean dissolved oxygen below the recommended WHO level. The ponds with the low dissolved oxygen were found within Lake Albert basin. Among the springs, Katanga spring (Kampala district, L. victoria basin) had mean dissolved oxygen that was below the WHO recommended level of 5 mg/L. Conductivities of the spring water were 89.81–3276.36 μS/cm and for ponds 55.99–3280.83 μS/cm. For both the springs and the ponds the differences between the lowest and the highest conductivities were wide.

Monthly variations of the springs and ponds water physicochemical characteristics

The monthly variations of spring and pond water physicochemical characteristics are shown in Fig.  4 .

Monthly variations of the physicochemical characteristics of the spring and pond water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) dissolved oxygen variations; Part d ) conductivity variations and Part e ) water turbidity variations

There were variations in the water physicochemical characteristics of the spring and the pond water overtime. The variations in water (springs and ponds) were also present between the different sites. The springs had small monthly variations of the water physicochemical parameters while the ponds had wide variations. Mughende pond (Kasese district) had the highest pH for most of the study period. Katanga spring (Kampala district) had the lowest pH compared to other springs during the study period. Kibenge spring (Kasese district) had higher temperature than the rest of the two springs (Katanga spring, Kampala district and Nyakirango spring, Kasese district). Most springs and ponds had slight fluctuations in dissolved oxygen except for Mughende pond (Kasese district). Most springs and ponds except for Panyimur pond (Nebbi district) had small monthly fluctuations in water conductivity. Kibenge spring and pond (both located in Kasese district) had higher conductivity compared to the rest of the springs or ponds. Mughende spring and pond were outliers with higher conductivity than the rest of the water sites. There were variations in water turbidity with months for both the springs and the ponds. Apart from Mughende pond (Kasese district), the rest of the springs and ponds showed variations that had two peaks, the first peak (May – August, 2015) and the second peak (November – January, 2016).

Test results of the other surface water sources: Mobuku irrigation canal water

Mobuku irrigation canal water, water diverted from Mobuku River for irrigation purposes by the Mobuku irrigation scheme was tested because the local communities were using this water for domestic purposes including drinking. Apart from water turbidity which was above the WHO recommended standard of 5NTU, the rest of the water physicochemical parameters (pH, temperature, dissolved oxygen and conductivity) were in the WHO acceptable range as follow: pH of 7.93 ± Standard Error (SE) of 0.23, temperature of 26.57 °C ± SE of 1.25 °C, dissolved oxygen of 6.38 mg/L ± SE of 0.18 mg/L, conductivity of 69.06 ± SE of 2.57) and turbidity of 28.68 ± SE of 9.06NTU.

Monthly variations of physicochemical characteristics of Mobuku irrigation canal water

There were monthly variations in water physicochemical characteristics of Mobuku irrigation canal. The water pH and dissolved oxygen showed two peaks each. The first peak was in March – May, 2015 and the second peak, August – November, 2015. The variations of the Mobuku irrigation canal monthly water physicochemical parameters over the study period is shown in Fig.  5 .

Monthly variations of the physicochemical characteristics of Mobuku irrigation canal water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) dissolved oxygen variations; Part d ) conductivity variations and Part e ) water turbidity variations

Results of statistical tests for the differences within sites overtime and between sites

One-Way ANOVA test.

There were no statistically significant differences within most of the study sites except for sites on the lakes and the rivers where the pH and temperature differences were statistically significantly within sites overtime. Statistically significant differences in the water physicochemical characteristics were observed between sites (all p -value < 0.05) as indicated in the additional file  2 .

Turkey’s post hoc test

There were statistically significant differences for all water physicochemical parameters for both the lake and river sites. For instance, Lake Edward had both the highest temperature (34 °C, May, 2015) which was registered at Katwe FLS (Kasese district) and the lowest temperature (18.9 °C, April, 2015) which was recorded at Kayanzi FLS (Kasese district). The results of the comparison of the physicochemical parameters of the various lake and river sites are shown in Table  4 .

Similarly, comparison of the springs or pond water showed statistically significant differences for most (80% of the total comparison) of the water parameters (pH, temperature, dissolved oxygen and conductivity) apart from the water turbidity. Turkey’s post Hoc test results for the comparison of springs and pond water physicochemical parameters are shown in Table  5 .

This study showed that water for drinking and domestic purposes from the surface water sources and springs in cholera affected communities/districts of Uganda were not safe for human use in natural form. The water samples from the water sources in the study area did not meet the WHO drinking water quality standards in terms of the important physicochemical parameters. In addition, all the surface water sources and the springs tested had turbidity above the WHO recommended level of 5NTU yet the same water were used for domestic purposes including drinking in the natural form by the households. The study also found variations in the other physicochemical parameters (pH, temperature, dissolved oxygen and conductivity) between study sites on the same lake and between the different water sources.

While the majority of the water sources had mean water physicochemical characteristics (excluding turbidity) in acceptable range, few water sources, mainly the sites on Lake George, including the springs and ponds had pH and dissolved oxygen outside the recommended WHO ranges. These water sources that did not meet the WHO drinking water standards could expose the users to harmful effects of unsafe drinking water including waterborne diseases such as cholera. The present study findings of high water turbidity if due to algae bloom could encourage pathogen persistence and infection spread, including V. cholerae bacteria [ 40 , 41 ] resulting in ill-health and cholera epidemics. In addition, the high water turbidity complicates water disinfection as it gives rise to significant chlorine demand [ 53 ]. The increased chlorine demand can be costly and difficult to ensure constant availability for disinfection of water since Uganda and several other developing countries need and receive supplementary donor support [ 69 ].

In regard to temperature, dissolved oxygen and conductivity, the majority of the surface water sources and springs tested met the recommended WHO drinking water standards. However, a few water sources such as River Lubigi in Kampala district had mean dissolved oxygen below the recommended WHO drinking water standards. Therefore, in order to ensure universal access to safe drinking water, the water sources that had vital physicochemical parameters outside the WHO drinking water range could be targeted for further studies.

There were statistically significant differences in the water physicochemical characteristics between the different sites and sources (lakes, rivers, springs and ponds). Despite these differences, the required approaches to ensure safe water access to the communities may not differ across sites. First and foremost, all sites and water types will need measures that reduce the high water turbidity to WHO acceptable levels. Secondly, in few instances, such as the water sources with pH in acidic range (Katanga spring in Kampala district, Lake Victoria Basin and Wanseko pond in Buliisa district, lake Albert basin) in addition to requiring further studies to identify the causes of the low pH (acidity), such water sources may also require the use of water treatment methods that neutralize the excess acidity [ 54 ]. Furthermore, since acidity is usually associated with increased solubility of toxic heavy metals (lead, arsenic and others) [ 34 ], testing such water for metallic contamination may be required. Heavy metal contamination of water causes ill-health due to chronic exposure which is cumulative and manifest late for correction to be done [ 70 ].

The findings of this study also highlight the differences in water quality between the urban surface water sources and springs (Kampala district) and the rural surface sources and springs (other study districts – Kasese, Kayunga, Busia, Nebbi and Buliisa) The water sources that met the WHO recommended drinking water quality standards [ 53 ] were mostly the rural springs and the rivers. However, these differences between the rural and the urban water sources do not alter the required approaches to ensure access to safe water which is by promoting measures that reduce the high water turbidity in combination with water disinfection to remove the pathogens. The relatively good quality of rural water sources compared to the urban ones could have been due to availability of plenty of vegetation in rural setting that filtered the water along the way downstream and possibly low level of pollution from industrial inputs in rural areas than in urban areas [ 71 , 72 ].

In relation to cholera outbreaks in the study communities, naturally, the physicochemical conditions for survival of V. cholerae O1 occur in an estuarine environment and other brackish waters [ 73 , 74 ]. In such circumstances, the favourable physicochemical conditions for V. cholerae isolation are the high water turbidity [ 49 ] and temperature of above 17 °C [ 43 ]. Interestingly, all the surface water sources and the springs tested had favourable physicochemical characteristics for the survival of V. cholerae in terms of these two parameters (high water turbidity and temperature of above 17 °C). Furthermore, two lakes sites (Kahendero FLS and Hamukungu FLS, Lake George, Kasese district) had also favourable mean pH for the survival of V. cholerae of 9.03 ± 0.17 and 9.13 ± 0.23 respectively. Favourable pH for V. cholerae survival in waters of Lake George was previously documented in the same area [ 23 ]. Hence, the frequent cholera outbreaks [ 19 , 20 , 21 , 24 ] in the study area could be attributed to both the favourable physicochemical water characteristics and use of unsafe water.

There were wide variations in conductivity between water sources and within the same source overtime. High water conductivities were recorded in the months of January to March 2015 (dry season), possibly due to high evaporation which increased the concentration of electrolytes present in water. Likewise, two rivers namely. River Lubigi (Kampala district) and Nyamugasani (Kasese district) had higher mean conductivities of 460.51 ± 57.83 μS/cm and 946.08 ± 3.63 μS/cm respectively than for typically unpolluted river of 350 μS/cm [ 75 ]. Consequently, given that the two rivers flow through areas of heavy metal mining (copper and cobalt mines in Kasese district by Kilembe Mines Limited and Kasese Cobalt Company Limited) and industrial activities (Kampala City), it is possible for the high water conductivity to be due to the heavy metal contamination as previously documented in drinking water in South-western Uganda [ 62 ] and Kampala City [ 61 ]. Thus, specific studies are required on water from the two rivers to determine the true cause of the high conductivity and to guide mitigation measures.

Hence, more efforts are required to promote safe water access in Uganda to attain the WHO cholera elimination target [ 25 ] and SDG 6 by 2030 since 26% (36/135) of mean physicochemical water tests did not meet WHO drinking water quality standards [ 53 ]. These findings together with those of the previous studies which demonstrated the presence of pathogenic V. cholerae in the same water sources [ 22 , 23 , 76 ] should guide stakeholders to improve access to safe water in the Great Lakes basins of Uganda holistically. Thus, measures such as promotion of use of safe water (using water disinfection), health education, sanitation improvement and hygiene promotion that address both the water bacteriological contents and physicochemical parameters should be considered in both the short and medium terms. However, long term plan to increase access to safe water by construction of permanent safe water treatment plants and distribution systems (pipes) should remain a top priority.

In the short and intermediate period, focusing on the measures that reduce water turbidity and disinfection of water (to kill microorganisms) should be prioritized so as to facilitate progress towards attainment of SDGs and cholera elimination in the study area. The basis for such prioritization lies in the fact that high water turbidity raises water temperature and prevents the disinfection effects of chlorine on water. These in return promote survival of the microorganisms and consequently cholera and other waterborne disease outbreaks. Furthermore, though boiling of water is feasible and recommended through technical guidelines [ 26 ] since it addresses both turbidity and kills the micro-organisms, it has issues of poor compliance due to lack of firewood which is the main cooking energy source in these communities [ 70 ]. Therefore, alternative safe water provision targeting reduction of high water turbidity and removal of microorganism by special filters such as decanting and sand filters and flocculation agents which do not need heat energy should be promoted [ 77 , 78 ]. Also, there is a need to explore the use of solar energy (solar water purifiers) [ 79 ] in these communities given their location in the tropics where sunshine is plenty. In the minority of situations, in addition to use of above methods to make water safe, there may be a need to employ different approaches of water purification depending on the water source. For example the water sources with lower or higher than recommended pH [ 53 ] (Wanseko pond, Hamukungu and Kahendero FLS on L. George), use of water treatment reagents that are affected by pH such as chlorine tablets should be reevaluated.

In additional to disinfection and turbidity corrective measures for all the water that were studied, each of the springs in the study area (Katanga in Kampala district and Nyakirango and Kibenge springs in Kasese district) will also need a sanitary survey (a comprehensive inspection of the entire water delivery system from the source to the mouth so as to identify potential problems and changes in the quality of drinking water) [ 80 ]. The findings of the sanitary survey should then guide the medium and long term interventions for water quality improvement in areas served by targeted springs. The following are some of the interventions that could be carried out after a sanitary survey: provision of a screen to prevent the entrance of animals, erecting a warning signs, digging of a diversion ditch located at the uphill end to keep rainwater from flowing over the spring area, establishment of an impervious barrier (a clay or a plastic liner) to prevent potential contaminants from entering into the water or and others measures described in the handbook for spring protection [ 81 ].

Furthermore, as a stopgap measure while access to safe water is scaled up, the communities in the study area should be protected from cholera using Oral Cholera Vaccines [ 82 ]. Protection of these communities is necessary since this study shows that favorable conditions for cholera propagation/transmission are present in the water in the study area. The favorable conditions that were documented in this study included the high water turbidity which makes it difficult to disinfect water [ 53 ] and the water temperature of above 17 °C which speeds up the multiplication of pathogens [ 43 ].

In addition, there were some other important study findings that were not fully understood. For example, some water sources (Kibenge spring and pond (located in Kasese district, western Uganda) had extreme vital physicochemical values for both conductivity and water temperature relative to the rest of above 40 °C and 3000 μS/cm respectively. It is possible that the extreme values were due to geochemical effects documented in water sources around Mount Rwenzori [ 83 ]. However, since there was copper and cobalt mining in Kasese district, high water conductivity could have been due to chemical contamination. Similarly, River Lubigi, Kampala district (central Uganda) had very low dissolved oxygen of less than 1 mg/L during some months (for example in January 2015, dissolved oxygen of 0.45 mg/L) which could have been due to organic pollutants from the communities in Kampala City [ 84 ] that used up the oxygen in the water. Also, Wanseko pond (Lake Albert basin, Buliisa district) had low pH of 4.84 in February 2015. Such water with low pH have the potential to increase the solubility of heavy metals some of which make water harmful when consumed [ 85 ]. Therefore, further studies will be required to better understand such extreme values.

Strength and limitations of this study

This study had several strengths. First, the longitudinal study design that employed repeated measurements of water physicochemical characteristics from the same site and source. This design reduced the likelihood of errors that could arise from one-off measurements seen in cross-sectional study designs resulting in increased validity of the study findings. Second, the inclusion of a variety of the water sources from which drinking and domestic water were collected namely, lakes, rivers, ponds, springs and a canal from different regions of Uganda made the findings representative of the water sources in study districts. Third, use of robust equipment, Hach meters, HQ40d [ 68 ] which automatically compensated for the weather changes (corrected for possible confounders and biases) for the parameters that had effect on each other such as raising water temperature impacting on the water conductivity and dissolved oxygen. Forth, purposive selection of the districts with frequent cholera outbreaks, an important waterborne disease that is targeted for elimination locally within Uganda and globally by WHO [ 25 ]. This meant that the findings had higher potential for used by stakeholders targeting to improve access to safe water and those for cholera prevention.

There were also some study limitations. First, though the study identified the favourable conditions (higher than recommended mean water turbidity and temperature of above 17 °C) for cholera in the study area, we could not report on causal-effect relationship between V. cholerae and the parameters studied. Vibrio cholera e pathogens were detected by use of multiplex Polymerase Chain Reaction (PCR). The results for PCR test were interpreted as positive or negative for V. cholerae O1, O139, non O1, and non O139 [ 22 ]. These data were not appropriate for establishment of causal-effect relationship Therefore, further studies using appropriate methods are recommended to establish such relationships.

Second, during some months of the study, water samples could not be obtained from some sources especially the ponds that had dried up during the dry season. The drying up reduced the number of samples collected from these points. However, since the months without water were few compared to the entire study period, the impact of the missing data could have been minimal.

Third, water samples were only tested for the five key physicochemical water characteristics, Vital Signs [ 32 ] however, there are many other parameters that effect survival and health of living things namely, nitrates, copper, lead, fluoride, phosphates, arsenic and others. Studies are therefore required to provide more information on these other parameters not addressed by the current study.

The study showed that surface and spring water for drinking and other domestic purposes in cholera prone communities in Great Lakes basins of Uganda were unsafe in terms of vital physicochemical water characteristics. These water sources had favourable physicochemical characteristics for transmission/propagation of waterborne diseases, including cholera. All test sites (100%, 27/27) had temperature above 17 °C that is suitable for V. cholerae survival and transmission and higher than the WHO recommended mean water turbidity of 5NTU. In addition, more than a quarter (27%) of lake sites and 40% of the ponds had pH and dissolved oxygen outside the WHO recommended range of 6.5–8.5 and less than 5 mg/L respectively. These findings complement bacteriological findings that were previously reported in the study area which found that use of this water increased their vulnerability to cholera outbreaks [ 22 ]. Therefore, in order for Uganda to attain the WHO cholera elimination and the United Nations SDG 6 target by 2030, stakeholders (the Ministry of Water and Environment, the local governments, Ministry of Health development partners and others) should embrace interventions that holistically improve water quality through addressing both physicochemical and biological characteristics. Furthermore, studies should be conducted to generate more information on the other physicochemical parameters not included in this study such as detection of the heavy metal contamination.

Availability of data and materials

The datasets generated and/or analysed during the current study are available in the Mendeley Data repository, https://doi.org/10.17632/57sw2w23tw.1 . The cholera incidence data used to identify the study area were from Uganda Ministry of Health and the district (Kasese, Busia, Nebbi, Buliisa and Kayunga) weekly epidemiological reports.

Abbreviations

Analysis of Variance

Conductivity

Central Public Health Laboratories

Dissolved Oxygen

Delivery of Oral Vaccines Effectively

Fish landing site

Institutional Review Board

Ministry of Health

Nephrometric units

Polymerase Chain Reaction

Sustainable Development Goal

Standard Operating Procedures

United States of America

World Health Organization

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Acknowledgements

The authors are grateful to the following: the district teams and the communities in Kasese, Kampala, Nebbi, Buliisa, Kayunga and Busia districts for the cooperation and support; the Ministry of Health, Makerere University School of Public Health, Dr. Asuman Lukwago, Dr. Jane Ruth Aceng and Prof. AK. Mbonye for technical guidance. The authors are grateful to Dunkin Nate from John Hopkins University for training of the field teams on water sampling and testing. The authors also thank Ambrose Buyinza Wabwire and to Damari Atusasiire for the support in creating the map and statistical guidance respectively. Special thanks to the laboratory teams in the district hospitals; CPHL (Kampala) and John Hopkins University (Maryland, USA) for carrying out the water tests.

This study was funded by the Bill and Melinda Gates Foundation, USA, through John Hopkins University under the Delivering Oral Vaccine Effectively (DOVE) project. (OPP1053556). The funders had no role in the implementation of the study and in the decision to publish the study findings.

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Godfrey Bwire, Henry Komakech & Christopher Garimoi Orach

Department of International Health, Johns Hopkins Bloomberg School of Public Health, Dove Project, Baltimore, MD, USA

David A. Sack, Amanda K. Debes, Malathi Ram & Christine Marie George

Uganda National Health Laboratory Services (UNHS/CPHL), Ministry of Health, Kampala, Uganda

Atek Kagirita

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GB, DAS, AKD and CGO conceived the idea. GB, CGO, AKD, MR, HK, AK, TO and CMG conducted the investigation. MR, HK and TO carried out data curation. MR, HK, GB, DAS, CMG, AKD and AK analysed data. GB, DAK, AKD, CGO, MR, AK, TO and CMG wrote the first draft. All authors read and approved the final manuscript.

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This study was approved by the Makerere University School of Public Health Institution Review Board (IRB 00011353) and the Uganda National Council of Science and Technology. Cholera data used in selection of the water bodies and study communities were aggregated disease surveillance data from the Ministry of Health with no personal identifiers. The laboratory reports on the water sources found contaminated during the study period were shared immediately with the district team to ensure that preventive measures were instituted to protect the communities. In addition, the communities served by such water sources were educated on water treatment/purification (filtration, boiling, chlorination, use of Waterguard ).

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Additional file 1..

The number and the type of water sources in each of the lake basins in cholera prone communities of Uganda that were enrolled in the study, February 2015 – January 2016.

Additional file 2.

One Way ANOVA test results for the differences within the study sites overtime (February 2015 – January 2016) and between sites.

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Bwire, G., Sack, D.A., Kagirita, A. et al. The quality of drinking and domestic water from the surface water sources (lakes, rivers, irrigation canals and ponds) and springs in cholera prone communities of Uganda: an analysis of vital physicochemical parameters. BMC Public Health 20 , 1128 (2020). https://doi.org/10.1186/s12889-020-09186-3

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‘Forever chemicals’ found to rain down on all five Great Lakes

FOR IMMEDIATE RELEASE

“The Ins and Outs of Per- and Polyfluoroalkyl Substances in the Great Lakes: The Role of Atmospheric Deposition” Environmental Science & Technology

Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS or “forever chemicals,” have become persistent pollutants in the air, water and soil. Because they are so stable, they can be transported throughout the water cycle, making their way into drinking water sources and precipitation. According to findings published in ACS’ Environmental Science & Technology , precipitation introduces similar amounts of PFAS into each of the Great Lakes; however, the lakes eliminate the chemicals at different rates.

Consuming PFAS has been linked to negative health outcomes. And in April 2024, the U.S. Environmental Protection Agency (EPA) designated two forever chemicals — PFOS and PFOA — as hazardous substances, placing limits on their concentrations in drinking water. The Great Lakes are a major freshwater source for both the U.S. and Canada, and the EPA reports that the surrounding basin area is home to roughly 10% and 30% of each country’s population, respectively. Previous studies demonstrated that these lakes contain PFAS. But Marta Venier at Indiana University and colleagues from the U.S. and Canada wanted to understand where the compounds come from and where they go.

Between 2021 and 2022, 207 precipitation samples and 60 air samples were taken from five sites surrounding the Great Lakes in the U.S.: Chicago; Cleveland; Sturgeon Point, N.Y.; Eagle Harbor, Mich.; and Sleeping Bear Dunes, Mich. During the same period, 87 different water samples were collected from the five Great Lakes. The team analyzed all the samples for 41 types of PFAS and found:

• ·In precipitation samples, PFAS concentrations largely remained the same across sites, suggesting that the compounds are present at similar levels regardless of population density.
• In air samples, Cleveland had the highest median concentration of PFAS and Sleeping Bear Dunes the lowest, suggesting a strong connection between population density and airborne PFAS.
• In the lake water samples, the highest concentration of PFAS were in Lake Ontario, followed by Lake Michigan, Lake Erie, Lake Huron and Lake Superior.
• ·The concentration of PFOS and PFOA in lake water decreased compared to data from previous studies as far back as 2005, but the concentration of a replacement PFAS known as PFBA remained high, suggesting that further regulation efforts may be needed.

The team calculated that airborne deposition from precipitation is primarily how PFAS get into the lakes, while they’re removed by sedimentation, attaching to particles as they settle to the lakebed or flowing out through connecting channels. Overall, their calculations showed that the northernmost lakes (Superior, Michigan and Huron) are generally accumulating PFAS. Further south, Lake Ontario is generally eliminating the compounds and levels in Lake Erie remain at a steady state. The researchers say that this work could help inform future actions and policies aimed at mitigating PFAS’ presence in the Great Lakes. 

The authors acknowledge funding from the Great Lakes Restoration Initiative from the U.S. Environmental Protection Agency’s Great Lakes National Program Office.

The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and all its people. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News . ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.

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Medical freedom vs. public health: Should fluoride be in our drinking water?

The culture wars have a new target: your teeth. 

Communities across the U.S. are ending public water fluoridation programs , often spurred by groups that insist that people should decide whether they want the mineral — long proven to fight cavities — added to their water supplies. 

The push to flush it from water systems seems to be increasingly fueled by pandemic-related mistrust of government oversteps and misleading claims, experts say, that fluoride is harmful.

“The anti-fluoridation movement gained steam with Covid,” said Dr. Meg Lochary, a pediatric dentist in Union County, North Carolina. “We’ve seen an increase of people who either don’t want fluoride or are skeptical about it.”

There should be no question about the dental benefits of fluoride, Lochary and other experts say. Major public health groups, including the American Dental Association , the American Academy of Pediatrics and the Centers for Disease Control and Prevention , support the use of fluoridated water. All cite studies that show it reduces tooth decay by 25%. 

“Drinking fluoridated water keeps teeth strong and reduces cavities,” the CDC said in a statement to NBC News. 

Still, the resistance to fluoride has been building for decades. More recently, the sticking point is about control.

It wasn’t “whether fluoride was good or bad,” said Brian Helms, a Union County commissioner who voted against adding fluoride to the local water supply in February. “The real deciding factor for my vote was a matter of consent.” He and others were swayed by people like Abigail Prado, the chair of a right-wing group called Moms For Liberty, who questioned the addition of fluoride in public water systems at Union County hearings on the issue.

“It’s the only treatment that the government just mass issues to its citizens,” Prado said in an interview. “That’s not right.” 

Union County, just south of Charlotte, is just the latest community to reject fluoridated water. Since 2010, more than 150 towns or counties throughout the country have voted to keep fluoride out of public water systems or to stop adding it, according to the Fluoride Action Network, an anti-fluoride group. 

Lawmakers in Georgia, Kentucky and Nebraska have filed bills that would end fluoride mandates in some of their larger communities. Within the past few months, local leaders in Collier County, Florida, and Amery, Wisconsin, voted to stop adding fluoride to public water systems. Last year, lawmakers in State College, Pennsylvania, and Brushy Creek, Texas, did the same.

A federal judge in California is considering whether health officials should stop adding fluoride to drinking water. There have been more than 100 lawsuits over the years trying to get rid of fluoride, without success, according to the American Fluoridation Society, an advocacy group. 

The anti-fluoride movement is troubling to doctors who treat children and others vulnerable to tooth decay.

“Community water fluoridation was revolutionary in terms of how it improved the oral health and dental health in our country,” said Dr. Charlotte Lewis, a professor of pediatrics at the University of Washington School of Medicine, with the “most dramatic effect in those populations that are lower-income and have less access to dental care.”

“I think we’re going to take big steps backwards,” she said.

How does fluoride work? How did it become the ‘bad guy’?

Bacteria in the mouth make acid, which weakens teeth and leads to decay. Fluoride counters that process in two ways: It reduces the amount of cavity-causing acids in saliva and strengthens enamel, the tooth’s protective outer layer.  

Applying fluoride directly to the teeth through toothpaste or rinses is important, but Lochary said small amounts circulating in the body are critical for young kids who still have their baby teeth. 

“Prior to the age of 6, you need to have some fluoride that you swallow so that it can get into the developing permanent teeth,” she said. “That’s the most important time for systemic fluoride.” 

It was in the early 1900s that experts first suspected something in the environment was affecting teeth. A dentist who moved from the East Coast to Colorado Springs, Colorado, noticed that people born in the area had dental anomalies he’d never seen before: teeth that were stained with dark brown spots but highly resistant to decay. 

Experts eventually discovered that the water in Colorado Springs had unusually high levels of fluoride — up to 12 milligrams per liter. Fluoride is a mineral found naturally in rocks, which then leaches into soil, rivers and lakes.

Grand Rapids, Michigan, became the first community in the world to add fluoride to its water supply in 1945. Within a decade, cavities among young children in the town had plummeted by 60% . 

Despite the dramatic reduction in cavities in kids, the Grand Rapids program was mishandled from the beginning. Residents weren’t immediately told that fluoride had been added to their water supply, leading to distrust in local lawmakers and their ability to make appropriate decisions about additives in the water. That triggered a pushback against fluoride in drinking water that has continued.

In 2015, the U.S. Public Health Service, under the Department of Health and Human Services, set the optimal level of fluoride in water at 0.7 milligrams per liter — a level that, after decades of real-world use, experts said, would help protect teeth without staining them.

As of this year, nearly two-thirds of the U.S. population with public water access use drinking water with fluoride, according to the CDC. 

A dramatic difference 

The positive impact of fluoride on kids’ teeth is easy to see, said Dr. Frank Courts, a pediatric dentist who has had offices in Ashe County, a rural community in Western North Carolina’s Blue Ridge Mountains, and in Nash County, a rural area east of Raleigh.

“The difference between the level of tooth decay in children is dramatic,” he said. 

His very young patients in Nash County tend to have fewer and smaller cavities. In Ashe County, children are significantly more likely to have permanent teeth so badly decayed that they have to be pulled before middle school, he said.

“Kids in high school have black front teeth,” Courts said of his practice in the western mountain region. “We see many young adults that have all their teeth already extracted and are wearing dentures in their 20s.”

Just over 10% of kindergartners in Nash County, which has added fluoride, had been treated for tooth decay in 2022-2023, according to the state Department of Health and Human Services . That percentage swelled to more than 44% in Ashe County, whose residents largely rely on nonfluoridated well and spring water. Both counties have similar income levels and rates of poverty. What explains the difference, Courts said, is that Nash County adds fluoride to its water supply. Ashe County doesn’t.

Even though Medicaid covers oral health for children, only 50% receive those services, said Dr. Julie Morita, executive vice president of the Robert Wood Johnson Foundation.

“People who don’t have access to dental care benefit even more from fluoridated water,” she said. “If they didn’t get fluoridated water, they’d be more likely to get cavities.”

The science behind fluoride

The fluoride issue goes well beyond medical freedom. The latest tactic used by anti-fluoride activists mirrors that of anti-vaccine groups: strike fear in the hearts of moms and dads.

Similar to the anti-vaccine movement, which has focused on disgraced research associating the mumps, measles and rubella shots with autism , groups opposed to fluoride tend to rely on one study that suggests the mineral is a neurotoxin that lowers children’s level of intelligence. 

A 2019 study, published in a well-respected journal, JAMA Pediatrics , found that IQ levels were slightly lower in 3- and 4-year-old children whose mothers had higher measures of fluoride in their urine when they were pregnant. Researchers concluded that pregnant women may want to avoid fluoride.

“We have a possible risk,” an author of the study, Dr. Bruce Lanphear, a professor of health sciences at Simon Fraser University in Canada, said in an interview. “It’s absolutely time for us to hit pause on this strategy.”

Lanphear stopped short of saying fluoride should be pulled from water supplies, and he said more research is needed. No other studies have shown similar findings. 

Even though a direct link has never been proven, the damage has been done, said Dr. Charlotte Lewis, a professor of pediatrics at the University of Washington School of Medicine.

“It doesn’t matter how much you try to dispel that,” Lewis said. “The onus is on us to continue to get that information out there. It’s a battle just like it’s a battle with the anti-vax folks.”

Dr. Donald Chi, a pediatric dentist at Seattle Children’s Hospital, said he has had to rethink how he talks with parents concerned about fluoride. The conversation starts not with data, but with empathy.

“There’s a lot of disinformation out there that preys on the vulnerability of parents,” Chi said. “People don’t want information. They just want to talk through it and process it.”

Richard Carpiano, a public health scientist at the University of California, Riverside, said, “This is an unintended consequence of parents being good parents.” 

Should pregnant women avoid fluoride?

The American College of Gynecologists and Obstetricians recommends that pregnant women use fluoridated toothpaste and mouth rinses to maintain their oral health, but it doesn’t take a position on fluoridated water.

Dr. Nathaniel DeNicola, an OB/GYN in private practice in Yorba Linda, California, hosts a podcast about possible effects of environmental toxins on pregnancy health. 

Microplastics, pesticides and air pollution are some examples. Fluoride isn’t.

“To be honest, fluoride doesn’t really rise to much attention when I’m counseling patients about things to be worried about in their drinking water,” DeNicola said. “Fluoride doesn’t fit in one of those categories we’re worried about.” 

Searching for solid evidence

The fluoride opposition argues there has never been a double-blinded, randomized, controlled clinical trial — the gold standard of scientific research — looking at the effects of fluoride on children. Researchers at the University of North Carolina, Chapel Hill, are recruiting 200 children under 6 months old to use either fluoridated or nonfluoridated bottled water in their formula and drinking water. Neither the researchers nor the families will know which kind of water will be given.

“I took that as a particular challenge,” said Gary Slade, a professor of dentistry at the Adams School of Dentistry at UNC-Chapel Hill.

The plan is to follow the children for four years to see how their teeth are developing. While the study isn’t funded to include a look at the kids’ IQ levels, it’s possible the study will expand, Slade said. 

“It is a perfect situation to look at the IQ of those children when they turn 4,” Slade said. “We’d still have time to add on that component to this study.”

Lochary said she regularly works to alleviate concerns among families who have heard that fluoride may be detrimental to kids.

“We get people who don’t want fluoride, and their kids will come in with a mouth full of decay. Then they won’t want us to do any treatment,” Lochary said. “I’m like, ‘Listen, dental infections can be very dangerous. You can end up in the hospital.’”

Erika Edwards is a health and medical news writer and reporter for NBC News and "TODAY."

Jason Kane is a producer in the NBC News Health & Medical Unit. 

Erin McLaughlin is an NBC News correspondent.

ORIGINAL RESEARCH article

Ecological and human health risk of heavy metals in nubui river: a case of rural remote communities, ghana.

• 1 University of South Africa, Pretoria, South Africa
• 2 Chair in Nanoscience and Nanotechnology, College of Graduate Studies, University of South Africa, Pretoria, South Africa
• 3 Nanosciences African Network, iThemba Laboratory, Cape Town, South Africa
• 4 University of Kinshasa, Kinshasa, Kinshasa, Democratic Republic of Congo
• 5 Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Johannesburg, Free State, South Africa

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The Nubui river is a primary source of water for drinking purpose and other domestic activities in the rural communities dotted along its riparian zone, with agriculture being the major activity occurring in this important ecotone. The river has become a potential sink for agrochemical residue, including heavy metals and has apparent aesthetic water quality issues, with associated health consequences. This study, therefore, assessed the health risks of heavy metals within the rural populations in the catchment areas, who have limited sources of improved water supply. The concentration of Iron (Fe), Lead (Pb), Cadmium (Cd), Mercury (Hg) and Zinc (Zn) was assessed on cumulatively 275 water samples, using a Perkin Elmer PINAAcle 900T atomic absorption spectrophotometer for eleven months. A cross sectional survey was conducted among 338 community members, following field observations on utilisation types, aesthetic appeal and perceived quality of water from the Nubui river. To determine the potential human and ecological risks of heavy metals, the hazard quotient, chronic daily Intake, contamination factor and health pollution indices of heavy metals were computed. STATA version 16 was used to analyse the survey results. Descriptive statistics of average concentrations of heavy metals in surface water at all sampling stations showed the pattern Hg ˂ Pb ˂ Cd ˂ Zn ˂ Fe, with relatively low concentrations, between 0.001mg/L-0.004 mg/L for Hg, 0.0011 mg/L -0.0019 mg/L for Pb, 0.0461 mg/L -0.0739 mg/L for Zn and 0.2409 mg/L -0.377 mg/L for Fe. The findings, however, showed relatively high Cadmium levels between 0.0215 mg/L -0.0383 mg/L in two out of five sampling stations in comparison to the World Health Organisation (WHO) drinking water guideline values in some months. Hazard quotient values indicate that, the population is safe from the noncarcinogenic health risks of heavy metals exposure through oral routes. Contamination factor and Heavy Metal pollution indices for Cadmium exceed recommended guideline values of 1 and 100 respectively. Meanwhile 73.1% community members evidently preferred the Nubui River for various domestic activities with 86.1% of these utilising it for drinking purposes. This occurrence, results in an exposure to associated health risks.

Keywords: Water Quality, heavy metals, health risk, Nubui River, Ghana

Received: 08 Mar 2024; Accepted: 13 May 2024.

Copyright: © 2024 Norvivor, Azizi, Fuku, Atibu, Idris, Sibali, Maaza and Kamika. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ilunga Kamika, University of South Africa, Pretoria, 0003, South Africa

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

'Forever chemicals' found to rain down on all five Great Lakes

Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS or "forever chemicals," have become persistent pollutants in the air, water and soil. Because they are so stable, they can be transported throughout the water cycle, making their way into drinking water sources and precipitation. According to findings published in ACS' Environmental Science & Technology , precipitation introduces similar amounts of PFAS into each of the Great Lakes; however, the lakes eliminate the chemicals at different rates.

Consuming PFAS has been linked to negative health outcomes. And in April 2024, the U.S. Environmental Protection Agency (EPA) designated two forever chemicals -- PFOS and PFOA -- as hazardous substances, placing limits on their concentrations in drinking water. The Great Lakes are a major freshwater source for both the U.S. and Canada, and the EPA reports that the surrounding basin area is home to roughly 10% and 30% of each country's population, respectively. Previous studies demonstrated that these lakes contain PFAS. But Marta Venier at Indiana University and colleagues from the U.S. and Canada wanted to understand where the compounds come from and where they go.

Between 2021 and 2022, 207 precipitation samples and 60 air samples were taken from five sites surrounding the Great Lakes in the U.S.: Chicago; Cleveland; Sturgeon Point, N.Y.; Eagle Harbor, Mich.; and Sleeping Bear Dunes, Mich. During the same period, 87 different water samples were collected from the five Great Lakes. The team analyzed all the samples for 41 types of PFAS and found:

• In precipitation samples, PFAS concentrations largely remained the same across sites, suggesting that the compounds are present at similar levels regardless of population density.
• In air samples, Cleveland had the highest median concentration of PFAS and Sleeping Bear Dunes the lowest, suggesting a strong connection between population density and airborne PFAS.
• In the lake water samples, the highest concentration of PFAS were in Lake Ontario, followed by Lake Michigan, Lake Erie, Lake Huron and Lake Superior.
• The concentration of PFOS and PFOA in lake water decreased compared to data from previous studies as far back as 2005, but the concentration of a replacement PFAS known as PFBA remained high, suggesting that further regulation efforts may be needed.

The team calculated that airborne deposition from precipitation is primarily how PFAS get into the lakes, while they're removed by sedimentation, attaching to particles as they settle to the lakebed or flowing out through connecting channels. Overall, their calculations showed that the northernmost lakes (Superior, Michigan and Huron) are generally accumulating PFAS. Further south, Lake Ontario is generally eliminating the compounds and levels in Lake Erie remain at a steady state. The researchers say that this work could help inform future actions and policies aimed at mitigating PFAS' presence in the Great Lakes.

The authors acknowledge funding from the Great Lakes Restoration Initiative from the U.S. Environmental Protection Agency's Great Lakes National Program Office.

• Nature of Water
• Nuclear Energy
• Environmental Issues
• Great Lakes
• Precipitation (meteorology)
• Evaporation from plants
• Lake effect snow
• Water resources
• Surface runoff
• Infiltration (hydrology)

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Materials provided by American Chemical Society . Note: Content may be edited for style and length.

Journal Reference :

• Chunjie Xia, Staci L. Capozzi, Kevin A. Romanak, Daniel C. Lehman, Alice Dove, Violeta Richardson, Tracie Greenberg, Daryl McGoldrick, Marta Venier. The Ins and Outs of Per- and Polyfluoroalkyl Substances in the Great Lakes: The Role of Atmospheric Deposition . Environmental Science & Technology , 2024; DOI: 10.1021/acs.est.3c10098

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• Research Article
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• Shantha Kumar Dhanush   ORCID: orcid.org/0009-0008-5532-9125 1 ,
• Mahadeva Murthy   ORCID: orcid.org/0000-0002-5776-9270 1 ,
• Sathish Ayyappa   ORCID: orcid.org/0000-0001-9739-6395 2 ,
• Devalapurada Kyari Prabhuraj 3 &
• Rinku Verma   ORCID: orcid.org/0000-0002-7024-6597 1  

An integrated approach combining water quality indices (WQIs), multivariate data mining, and geographic information system (GIS) was employed to examine the water quality of Bheemasandra Lake, located adjacent to a sewage treatment plant (STP) in Tumakuru city, India. The analysis of 22 lake water samples, examined before and after the monsoons, revealed that the physicochemical parameters namely — electrical conductivity, biochemical oxygen demand, turbidity, total dissolved solids, ammoniacal nitrogen, nitrates, phosphates, magnesium, total hardness, total alkalinity, and calcium — exceeded the acceptable limits stipulated by national and international standards. The Canadian Council of Ministers of the Environment WQI (pre-monsoon: 25.3; post-monsoon: 33.9) and weighted arithmetic WQI (pre-monsoon: 3398; post-monsoon: 2093) designated the water as unsafe for drinking. Irrigation WQIs (sodium adsorption ratio, sodium percentage, residual sodium carbonate, magnesium hazard, permeability index, and potential salinity) implied water’s suitability for irrigation. However, electrical conductivity indicated otherwise. Industrial WQIs (Larson–Skold Index, Langelier Index, Aggressive Index, and Puckorius Scaling Index) illustrated scaling propensity and the chloride sulfate mass ratio alluded galvanic corrosion potential. Hierarchical cluster analysis gathered 22 sampling points into two clusters (cluster 1: relatively lower polluted regions; cluster 2: highly polluted regions) for each season based on similarities in water features. Principal component analysis extracted four (79.07% cumulative variance) and six (87.14% cumulative variance) principal components before and after the monsoons, respectively. These components identified the primary pollution sources as urban sewage and natural lithological processes. WQI maps, created using the inverse distance weighted interpolation technique, enhanced the visualization of spatial–temporal variations. This study highlights the dire consequences of urbanization, STP pollution, and sewage management failures, necessitating that concerned authorities should implement policies and measures to curb the negative impacts on the environment and public health.

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The data supporting the findings of this study are available within the paper and its supplementary information/online resource file available from the figshare repository: https://doi.org/10.6084/m9.figshare.25587474.v2 (Dhanush et al. 2024 ).

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Acknowledgements

The authors are greatly thankful to Sarvath, Darshan, and Jeevan (Water testing laboratory, Department of Forestry and Environmental Science, University of Agricultural Sciences, GKVK, Bangalore) for handling and transporting water samples. Furthermore, we thank Vinay and Nithin (Department of Soil Science and Agricultural Chemistry, University of Agricultural Sciences, GKVK, Bangalore) for their invaluable tips in remote sensing aspects.

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Shantha Kumar Dhanush: conceptualization, methodology, formal analysis, investigation, writing – original draft, writing – review and editing. Mahadeva Murthy: formal analysis, resources, writing – review and editing. Sathish Ayyappa: software, visualization, writing – review and editing. Devalapurada Kyari Prabhuraj: visualization, resources, writing – review and editing. Rinku Verma: visualization, writing – review and editing.

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Dhanush, S.K., Murthy, M., Ayyappa, S. et al. Water quality assessment of Bheemasandra Lake, South India: A blend of water quality indices, multivariate data mining techniques, and GIS. Environ Sci Pollut Res (2024). https://doi.org/10.1007/s11356-024-33670-7

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A Global Challenge: Clean Drinking Water

Xiuqiang li.

1 Department of Mechanical Engineering and Material Science, Duke University, Durham NC, 27708 USA

Hui Ying Yang

2 Engineering Product Development Pillar, Singapore University of Technology and Design, Singapore 487372 Singapore

Water is an essential element for life. A minimum of 5L/day of drinking water is required for a person to survive with normal activities. [ 1 ] Currently, 2.1 billion people globally have limited access to safe drinking water. Additionally, about 6% of deaths in underdeveloped countries are caused by drinking unsafe water. [ 2 ] To address water scarcity, the research community has proposed a variety of solutions to alleviate the drinking water crisis, such as solar desalination, reverse osmosis (RO), atmospheric water harvesting, and capacitive deionization technology (CDI). However, the high energy consumption, low efficiency and/or high production cost of these technologies greatly hinder the future development of these devices. However, with the development of material science and nanotechnology, some profound changes are taking places in these technologies. This special issue features four review papers and three research papers that focus on solar desalination, atmospheric water harvesting and CDI for clean drinking water, which aim to further promote the development of related technologies.

Direct solar desalination, which produces freshwater directly using solar energy with minimum carbon footprint, is considered to be one of the most promising technologies to alleviate the water shortage crisis. However, the traditional bulk water heating method is inefficient (≈40%). Recently, interfacial solar vapor/steam generation has been proposed to improve heat localization at the liquid surface and has achieved ≈90% solar‐to‐vapor conversion efficiency under 1 Sun. In this special issue, a review paper contributed by Irshad et al. (article number 2000055) systematically summarizes the progress of solar vapor/steam generation and constructively points out the key directions of future research. As mentioned in this review, the long‐term stability of absorbers is still a challenging issue. Zhuang et al. (article number 2000053) and Gu et al. (article number 2000063) demonstrate two advanced materials, reduced graphene oxide hydrogel membranes and three‐dimensional honeycomb chitosan‐based aerogels, which exhibit long‐term stability without compromising the water evaporation rate (> 1.7 kg m −2 h −1 ). These represent competitive materials for salt‐resistant absorbers. Meanwhile, an impressive work hoping to thoroughly solve the problem of salt‐rejecting of absorbers is presented by Bian et al. (article number 2000077) who select a highly efficient selective absorber and use convection between the selective absorber and water to heat the water (the absorber was suspended above the water instead of traditional direct contact). The results show that the evaporation efficiency is able to reach 1.94 kg m −2 h −1 . Additionally, it is worth noting that the advantages of the regulation and utilization of infrared light have been reported recently, with the use of selective absorbers to obtain higher efficiency, and the use of radiative cooling to enhance condensation, etc., becoming a key focus for researchers. In this special issue, Li et al. (article number 2000058) offer a fundamental understanding of spectrum design, alongside a discussion of recent progress and future directions of for this research.

Atmospheric water harvesting, which captures the moisture from air and then condenses the captured moisture into liquid water, is a promising technology to resolve the water crisis in arid regions. Compared with traditional inorganic salts, zeolites, etc., recently developed materials, such as MOFs/COFs and hydrogels, are demonstrated to have lower desorption energy and/or humidity adsorption. In this special issue, Zhuang et al. (article number 2000085) contribute a review paper to discuss and provide a perspective regarding various atmospheric water harvesting technologies, especially for solar atmospheric water harvesting with the above‐mentioned advanced materials. In addition, CDI technology is also a competitive technology that uses electrode materials to extract positive and negative ions in the feed solution to achieve water purification. Liu et al. (article number 2000054) review various sodium‐ion intercalation materials as highly efficient CDI electrodes, and provide some instructive perspectives. We believe that these papers will be helpful for both the research and industrial community to achieve new milestones and to shape future research directions.

As United Nations Development Programme 6 mentions, [ 3 ] with the increase of drought and desertification, more and more countries will suffer from water shortages. By 2050, it is predicted that at least one in four people will suffer from recurring water shortages. Herein, learning from the perspectives of the authors in this special issue, we believe that more efficient devices based on new mechanisms, new materials, and new structures should be developed. In addition, the stability and price of the devices need to be considered in the long‐term research and industrial plan. The community should also actively communicate and collaborate with industry and the public to apply these advanced technologies into practice to alleviate the drinking water challenges of the future.

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Hui Ying Yang, Email: gs.ude.dtus@gniyiuhgnay .

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