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Water, Water, Everywhere

How Much Water Do You Really Need to Drink?

WebMD Feature

April 16, 2001 -- You'd think we were suffering a nationwide drought, the way Americans go around clutching bottles of water these days. Forget American Express cards: The one thing many of us would never dream of leaving home without is our bottled water.

By all rights, that should be good news. For years nutritionists have been warning us about the dangers of dehydration. Quaff at least eight 8-ounce glasses of water, the common wisdom goes, or you'll suffer the consequences: flagging energy, dry skin, lowered disease resistance, even constipation.

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And don't count the coffee, tea, or other caffeinated beverages you drink. Anything with caffeine, we've long been told, actually increases the risk of dehydration because it flushes water out of the system.

Nor can you rely on thirst. By the time you're thirsty, you're well on your way to being dehydrated.

There's only one problem with all these warnings. Almost none of them hold water. Here's why:

Myth No. 1: We need to drink at least eight 8-ounce glasses of water a day

Researchers aren't sure where this familiar advice came from, but most agree there's very little solid scientific evidence to support it. The average adult loses only about 1 liter of water a day through sweating and other bodily processes -- the equivalent of only four 8-ounce glasses. We typically get that much water just in the foods we eat. Drinking an additional eight tall glasses of H20 is probably more fluid than most of us need.

What about older people? For years, experts have warned that elderly people are especially prone to dehydration because they lose their sense of thirst. But even this may be overstated, according to a report in the July 2000 Journal of Gerontology. Robert Lindeman, MD, professor emeritus of medicine at the University of New Mexico, surveyed fluid consumption among 833 elderly volunteers.

"People who drank less than four glasses of water a day were no more likely to show signs of dehydration than those who drank six or more," says Lindeman. "We found absolutely no difference between those who drank a little and those who drank a lot when we looked at all the standard markers for dehydration."

Of course, that doesn't mean you shouldn't drink plenty of water a day. In fact, there's at least one reason to think it's a very good idea. In a 1999 study published in The New England Journal of Medicine, researchers found that the more liquids men consumed, the lower their risk of bladder cancer. Men who drank more than 10 8-ounce servings of fluids had a 49% lower incidence of the disease than those who drank only half that much.

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