(HealthScoutNews)-- The mantra on daily water consumption may be a washout.

When you ask for advice on how much of the clear, cool liquid you should swig each day, there's a good chance you'll hear the following: At least eight 8-ounce glasses, or 64 ounces, of water each day.

But a New Hampshire doctor says that advice is hogwash, a national myth with no basis in physiologic fact.

Dr. Heinz Valtin, of Dartmouth Medical School, has researched the matter of adequate water intake and found a desert of evidence in support of the "8 x 8" theory.

Instead, Valtin says, those 64 ounces a day will get you little farther than the bathroom. In rare cases, people who drink too much may suffer "water intoxication" by overloading their kidneys. This phenomenon has been seen in athletes, Ecstasy users and even healthy people.

True, some of us may indeed need that half-gallon of water on some days -- when we're working out in the heat or flying for long distances in a dry airplane cabin. However, those situations appear to be the exceptions, not the norm.

"I have found no scientific proof that absolutely every person must drink at least eight glasses of water a day," says Valtin, a kidney specialist, in a statement. His review of the subject appears in the latest Internet edition of the American Journal of Physiology.

Valtin says the 64 ounces-a-day figure might have been a bastardization of recommendations from the National Research Council's Food and Nutrition Board, which in 1989 called for roughly a milliliter of water coming in for every calorie of energy expended.

However, the guidelines go on to state that most of that amount -- 64 ounces to 80 ounces, on average -- can be obtained in prepared foods that are rich in fluids.

Items like juice, milk, soda and coffee are almost entirely water and may be reasonable substitutes for glasses of the plain stuff, Valtin says.

Yet, while the origins of the 8 x 8 myth are murky, the booming bottled water industry is clearly a driving force behind its promotion. Witness water.com, which boasts of being "the first e-commerce site for the purchasing and delivery of high quality spring water."

A "Live Healthy" section of the site, part of the Suntory Water Group in Atlanta, declares that "most experts agree that eight 8-ounce glasses is a good rule of thumb. But every individual has his or her own needs, and the amount of water needed from person to person varies, depending on their weight and level of activity."

However, it seems the only variable is how much more than 64 ounces a day you need. On a water intake calculator water.com provides, a 160-pound person who got no exercise is advised to drink 80 ounces, or between six and seven 12-ounce glasses, a day. Adding a 20-minute workout to the routine ups that figure to 84 ounces.

Stephen Kay, a spokesman for the International Bottled Water Association, says the 8 x 8 recommendation "certainly was not invented by the bottled water industry, nor is it a bottled water issue only. The issue overall is really water and water consumption" for proper hydration.

While a variety of foods have fluids, Kay says water is the "most direct source" of, well, water. It also happens to be free of calories, caffeine and other potentially undesirable substances. A statement on the group's Web site in response to Valtin's paper says it "remains supportive" of the 8 x 8 guidelines.

The Food and Nutrition Board is now reviewing daily water consumption. Its recommendations should be released in March 2003, says Paula Trumbo, a nutritionist who's in charge of the project.

Trumbo says her group is not relying on Valtin's paper, since it's a review not a study. However, she adds she agrees so far with his conclusion that there's little data supporting the conventional water wisdom.

"No one really knows the scientific basis for" the 8 x 8 rule, Trumbo says. "It's kind of hard to say whether it's credible or not."

The panel is conducting a study to clear up the question of how much water a person needs. Whatever answer emerges is sure to vary by weight or climate, for example, she says.

They're also looking at how, if at all, water intake affects certain health outcomes, from kidney stones to heart ailments, and whether the fluid in foods such as fruits and vegetables is an adequate source of H2O.

"We will be very specific in saying what this value is for," Trumbo says.

What To Do

For more on water and health, try the University of Iowa. For the water industry's perspective, visit the International Bottled Water Association.

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