You Can Drink Too Much Water

Conventional wisdom is to drink eight glasses of water, about eight ounces each, every day. Not only does the “eight by eight” rule lead to lots of time in the rest room, but drinking so much water is not necessarily good for you. According to Arthur J. Siegel, MD, director of Internal Medicine at McLean Hospital in Belmont, Massachusetts, most people do better simply drinking to thirst, and that’s especially true during prolonged exercising.


We all know that hydration is critical to health. It helps to maintain stable body temperature by replacing fluid losses in sweat, thereby supporting blood flow to vital organs, including the brain, but there can be too much of a good thing. Investigating the deaths of two marathon runners from water intoxication during the 2002 Boston and Marine Corps Marathons, Dr. Siegel and researcher colleagues discovered that their exercise-associated hyponatremia (EAH)—the medical term for having too much water in body fluids relative to sodium concentration—was triggered not just by how much they drank but also a hormonal imbalance, sometimes related to exercising for many hours, that prevented the kidneys from excreting excess water. Guidelines from the American College of Sports Medicine now address prevention of both excessive dehydration and hyponatremia, emphasizing that there is considerable variance among individuals, activities and environmental conditions that affect hydration needs. Elite athletes and people exercising for endurance (triathletes, for instance) should drink ahead of thirst and consider consuming salt-enhanced sports drinks or other similar products instead of plain water. Discuss specific hydration strategies under these circumstances with your doctor, as individual needs vary.

Fluid retention can be a major problem, especially for slower recreational athletes, even drinking at over one liter/hour for more than four or five hours. “Acute water intoxication” is overhydration, which can result when the intake of any dilute fluid, including sports drinks, exceeds the capacity of the kidneys to excrete the excess water in urine, which may be limited by the hormonal imbalance during exercise.

Not as rare as you might guess, this condition was found in 13% of 488 study participants in the 2002 Boston Marathon, most of whom were slower runners who avidly consumed fluids, including sports drinks. The International Marathon Medical Director’s Association has since issued a fluid recommendation suggesting non-elite runners try to “drink to thirst.” According to Dr. Siegel, this is good advice for most people, even those who are sedentary.


Almost all noncaffeinated fluids will keep you hydrated, but the vast majority of people should mostly drink water. Sports drinks marketed for their ability to replace sodium and other electrolytes aren’t necessary and can even be dangerous, since salt replacement with too much water intake can be hazardous. “The risk of overhydration is all about too much water, not too little salt,” says Dr. Siegel.

So, exercise notwithstanding, how much water should we drink during the course of a normal day? Daily Health News contributing medical editor Andrew L. Rubman, ND, said one easy way to tell if you’re properly hydrated is to check the color of your urine. “It should be the color of light straw,” he said. If your urine is dark and highly concentrated, take that as a cue to drink more water. If it is colorless, you may be drinking too much.

Dr. Rubman agrees with Dr. Siegel—thirst is usually a good guide to determine how much we should drink. He noted, however, that elderly people may lose their ability to perceive thirst and forget to drink water regularly. They may need reminders to keep sipping, thirsty or not. Two to three pints a day is a good minimum goal—set out a jar filled with this amount each morning, and make sure it is finished by bedtime. Also, increased thirst and urination are signs of high blood sugar in patients with diabetes mellitus, who need to take special care to maintain their intake, especially during heat waves.

Also, since thirst can sometimes be misperceived as hunger and lead to overeating, Dr. Rubman suggests it’s a good practice to drink a glass of water if you think you’re hungry but have recently eaten good-quality food. While on the topic of drinking, Dr. Rubman also noted that you should never drink too much with a meal, but for an entirely different reason. Proper digestion requires production of adequate stomach acid to activate enzymes—water can interfere with that process, he says. Best to sip gently during meals, and wait an hour or more afterward to satisfy a big thirst.