How Much Water Should I Drink?

A kidney specialist and professor at Dartmouth Medical School, Dr. Heinz Valtin, wrote in the American Journal of Physiology that after he and his colleagues became concerned by the numerous articles published that promoted sipping water all day, he could find not a single scientific study that substantiated the “8x8" rule. He noted that the National Research Council's Food and Nutrition Board recommended in 1945 drinking one milliliter of water or other non-diuretic beverage for each calorie of food consumed on a 2,000-calorie diet. The Council, however, observed that much of the suggested volume is contained in food and it should be considered with regard to total water consumed. The NRC water consumption advisory made public a half century ago was the only official recommendation he uncovered in his research. Other specialists in nutrition and body water balance searched through electronic research databases to double-check the work of Dr. Valtin, and they found no evidence to suggest the need for drinking 64 ounces of water per day. 

Dr. Valtin acknowledged that certain diseases, such as kidney stones, do require drinking greater amounts of water (sometimes--ask your physician) than normal, but concluded that most people (healthy, mainly sedentary adults in temperate climates) do not need to drink the large amounts of water advocated by “…someone misinformed…." He maintained that drinking enough water to satisfy thirst, including coffee, tea, and other beverages, is adequate for average circumstances, while vigorous work or exercise, especially in hot climates, justifies a greater intake of water.

His credentials—more than four decades of research on the body method that controls water diffusion through the cells, the osmoregulatory system—make Dr. Valtin a highly-qualified subject matter expert regarding human needs for water consumption. So, how much is too much?  Read on...

There is danger in over-hydration, or overdosing, with large quantities of water or other fluids, particularly when consumed in a brief time period. This can cause a life-threatening condition called hyponatremia, sometimes referred to as water intoxication, which occurs when too much sodium has been displaced in the blood. There are documented deaths from large intakes of water too quickly, a situation more likely to occur when marathon runners drink gallons of water without replacing electrolytes. Drinking too much water in this manner overwhelms the kidneys, which cannot get rid of the extra water quickly enough to prevent electrolyte imbalance. Water ultimately enters the cells, which swell to accommodate it. When brain swelling occurs, the skull allows no room for expansion, which causes seizures, coma, or even death.

In addition to intense exercise, here are some other risk factors for hyponatremia: (1) the small body mass of babies under nine months of age that puts them at increased threat in a briefer span of time, if, for example, an infant is given several bottles of heavily-diluted formula in a day; (2) regular ingestion of certain medications, such as diuretics (water pills), pain medications, or antidepressants that cause increased urination or perspiration; (3) hormonal changes of the thyroid or adrenal gland that affect the body's ability to maintain its electrolyte balance; (4) age-related changes in the elderly that may alter the body's sodium balance; (5) any person on a sodium-restricted diet whose blood sodium level may already be affected; (6) competitive eaters who often train for contests by drinking large amounts of water for rehydration during short periods; (7) a person with undiagnosed or untreated diabetes insipidus; and (8) use of the recreational drug, Ecstasy, an amphetamine that increases the danger of severe hyponatremia and even death.

There is no “one-size-fits-all" water drinking formula. Several factors can impact how much water an individual may need, and these are situational. Exercise is one, and a hot environment is another. Even when exercising intensely for more than an hour (such as when running a marathon), no more than 30 ounces of water should be consumed hourly, and sports drinks rather than plain water can help keep the body's potassium and sodium at the appropriate levels. Anyone engaging in work or activity outdoors that causes sweating for shorter periods should replace lost fluids by drinking an extra cup or cup-and-a-half of water.

Acute illness with fever and gastrointestinal involvement may cause a higher than normal loss of body fluids. Bladder infections or urinary tract stones usually call for increased water intake. Pregnant or breastfeeding women need additional fluids to ensure adequate hydration. 

Conversely, congestive heart failure and some types of kidney, adrenal, and liver diseases may cause the body to retain fluids and require the limitation of water intake. Illnesses that may affect the body's electrolyte balance, whether acute or chronic, should be monitored and treated by a physician.

Although not common, there are tragic examples of death due to water overdoses that caused hyponatremia. In 2005, a 21-year-old man died after being forced to drink excessive amounts of water during a fraternity hazing at California State University.

Another fatal overdose of water occurred in 2007 when a California radio station held an ill-advised on-air contest of competitive, excessive water drinking with no bathroom breaks allowed. A 28-year-old mother of three died after downing six liters of water in three hours and not being allowed to use the restroom. She did this in the quest to win a Nintendo game console, taking second place for a pair of concert tickets. Leaving the radio station complaining with a severe headache, she went home and called into work sick, dying in her bathroom only a few hours after the contest ended. A jury's $16.5 million judgment against the radio station in a wrongful death lawsuit filed by the woman's husband was unlikely to be much comfort to her children, but may prevent other corporations from engaging the public in such dangerous activities. What her husband told "Good Morning America" afterwards was just unbelievable. Read on...