Advice on water doesn't hold water

"Now, wait a second!" he says. "You doctors have been telling us to drink eight glasses of gravy a day!"

If that's how people are getting their advice on how much water to drink, doctors say it's time to stop looking for advice.

Two kidney specialists at the University of Pennsylvania, Drs. Dan Negoianu and Stanley Goldfarb, searched through the existing research on water consumption -- and found there's surprisingly little out there.

For starters, where did you hear that we ought to drink an eight-ounce glass eight times a day?

"From my fourth-grade science teacher," said a young man we asked on the street in Philadelphia.

"I think I heard it from my mom," said a woman in New York.

In fairness, your mother wasn't wrong, but Negoianu and Goldfarb say there's no real evidence she was right either. As best they could tell, there really wasn't much evidence at all.

"We set out to take a look at the eight-by-eight myth, and we were really unable to find any scientific rationale for it," Goldfarb told ABC News.

Will water make you feel full so that you'll eat less while dieting? The doctors were only able to find two small studies -- which disagreed.

Neither are there many studies to say that guzzling water will prevent headaches or flush toxins from your body.

"I always laugh when I hear that one," says Stella Volpe, a nutritionist at the University of Pennyslvania School of Nursing. "Your kidneys do that job." Volpe was not involved in today's study, which is published in the Journal of the American Society of Nephrology, an organization of kidney specialists.

So why did these notions take hold? Goldfarb says they found medical-advice sites on the Internet are full of recommendations to drink extra water.

"It's required for life, and I guess that's led people to think, well, if a normal amount is good, then extra might be better," he said.

More is of course better if you're working out, or if you're in a hot, dry climate. But most of us, say the researchers, get all we need in our daily diet.

A 2004 paper from the Institute of Medicine, part of the National Academy of Sciences, recommended that women average 91 ounces of fluid a day, and that men get about 125 ounces.

At first glance, that sounds like 11 to 16 glasses -- but Volpe, who was on the panel that came up with the numbers, says you get more than what you need from water, coffee, soda and soup. And she reminds people that 20 percent of their daily water is from solid food, much of which contains water.

"Drink when you're thirsty," said Goldfarb. "That's the way your body is designed."

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