Here's a quick health quiz: How much water does the average adult need to drink every day to remain healthy?
a) Four glasses. b) Eight glasses. c) Don't know.
Here are the answers:
a) You're right. b) You're right, too. c) You may be even closer to the truth than if you answered four or eight glasses.
Most Americans — 63 percent in a survey released in February by the International Bottled Water Association — have been told eight 8-ounce glasses of fluid are optimal to keep the body properly hydrated.
But there does not appear to be any one scientific study specifying that number. Nutritionists, historians, government agencies and makers of bottled water could not cite one when we asked.
"It's a bit of a mystery, " says Barbara Rolls, a professor of nutrition at Penn State University. "For scientists, academics, to have to admit they don't know the origin of something is very frustrating," she laughed.
Apparently, say scholars, eight-glasses-a-day is advice that's become accepted wisdom simply because it has been repeated so often. The National Academy of Sciences did issue guidelines in 1989, currently under review, for water consumption — but it used a formula for how much water one needs, based on how many calories one uses up. No help there in tracing the origin of the eight-glasses rule.
"It probably started very long ago," said Barbara Levine, a nutritionist at Rockefeller University in New York City, "but I can't pinpoint it. I think I have a book on my shelf from the 1920s that makes a reference to it."
It's important to say that if you're generally in good health, water cannot be bad for you. Doctors say it helps digestion, maintenance of body temperature, and removal of metabolic waste. If you drink more than your body needs, your kidneys will quickly get rid of the excess.
And if it's good for you, it's even better for the companies that sell bottled water. It is the fastest-growing drink in America; by 2005, analysts predict, it will be outselling coffee or milk.
Generally, nutritionists say if water displaces the empty calories of most soft drinks, fine. But eight glasses?
"Drinking water instead of sugary drinks, for most of us, is a good thing," says Rolls. "But do we need to be carrying a water bottle around all day? I don't think so."