Water is good for body and soul, but you don't need to drink as much as you might think. Here's the truth about what's enough, plus five other myths about water.
By Catherine Guthrie
For the past 50 years, nutritionists and other health experts have been exhorting Americans to drink more water. And if the ubiquity of the water bottle is anything to go by, this message has been heard loud and clear. Everywhere you look—college campuses, commuter trains, yoga classes—you see the plastic water bottle in all its variations.
But now that it's been firmly established in your psyche, and you either dutifully swig water constantly or feel guilty for not doing so, new research lets you off the hook. As it turns out, much of the water craze springs from a deep well of misinformation. Our experts debunk some of the most popular water myths and relieve your guilty conscience in the process.
MYTH: You need eight 8-ounce glasses of water a day to be healthy.
TRUTH: The familiar "8 x 8" rule is based not on ironclad scientific certainty but more likely on a misinterpreted recommendation from the 1940s, says Heinz Valtin, M.D., a kidney specialist and retired professor at Dartmouth Medical School in Hanover, New Hampshire. Valtin traces the prescription to a 1945 recommendation by the Food and Nutrition Board of the National Research Council to take in "1 milliliter for each calorie of food."
The problem, as Valtin explains in an American Journal of Physiology study in 2002, is that most of that allotment already comes from the foods we eat. He not only pooh-poohs the need for most people to consume eight 8-ounce glasses of water every day but also writes that the recommendation is potentially harmful "in making people feel guilty for not drinking enough."
The crux of the miscalculation hinges on the definition of water. "The consumer ended up thinking only plain water counts," says Ann Grandjean, Ph.D., a hydration researcher and the executive director of the nonprofit Center for Human Nutrition in Omaha, Nebraska. But almost all liquids—including tea, coffee, and beer—count toward the daily water intake, she says.
So, how much should you be drinking? If you would like hard and fast guidelines, you can follow the advice of the National Academies' Institute of Medicine, which reconfigured its recommendations for water intake last February. After reviewing more than 400 studies, including Valtin's, the authors set the general daily intake for women at roughly 91 ounces and for men at approximately 125 ounces.
But remember, these numbers include both food and water. The average American gets 20 percent of his or her water intake from food. Even spaghetti is 66 percent water (see the chart at the end of this article). The remaining 80 percent comes from all beverages. Taking that into account, by the institute's reckoning a woman should drink 72.8 ounces (nine 8-ounce glasses) daily and a man 100 ounces (12.5 glasses). But, unlike what you may have heard before, those 72.8 ounces can come from coffee, tea, or soda—not just water.
MYTH: Caffeinated beverages zap your body's water reserves.
TRUTH: Grandjean first became interested in the reputed link between dehydration and caffeine while working as a consultant to the United States Olympic Committee. "I worked with elite-level athletes, and I noticed they drank a lot of caffeinated beverages without showing any sign of dehydration," she says.
In 2000, she published a study on caffeine consumption and hydration in the Journal of the American College of Nutrition. For the study, Grandjean and her colleagues recruited 18 healthy men and on various days had them drink 59 fluid ounces of liquid that included varying amounts of plain water, diet cola, and coffee, depending on subjects' body mass. Researchers tested each participant's body weight, urine, and blood before and after drinking. The authors discovered the body doesn't discriminate between regular and decaf beverages when it comes to hydration. After the study exonerated caffeine, Grandjean, like Valtin, was stunned by the public's reaction. "Consumers started calling and saying 'This is wonderful,' " she recalls with a chuckle. "All those closet caffeine addicts—it was as if they'd all been liberated."
MYTH: If you're thirsty, you're already dehydrated.
TRUTH: While thirst is an accurate barometer of when to imbibe, the notion that thirst signals a dehydrated body is not true, says Valtin. Dehydration occurs when the blood's concentration of solid particles rises by 5 percent. Thirst is triggered when blood concentration rises by 2 percent. So thirst sets in before dehydration. (The exception is older people, who may not feel thirsty even when they're slightly dehydrated.)
That said, the fact that you're not dehydrated yet is no reason to avoid water. "Thirst is the first indicator of the body's need for water," says Dee Sandquist, spokesperson for the American Dietetic Association. And people who shrug off their thirst will find themselves on the path to dehydration. Signs to look for include headache, dry mouth, rapid pulse, and light-headedness.
MYTH: Urine should be clear.
TRUTH: Perpetually clear urine can actually be a sign of drinking too much water, which can dilute the body's electrolytes, according to Grandjean. "Healthy urine should have some color," she says. Certain vitamins, such as riboflavin (B2), can darken urine. If the flow is unusually dark or cloudy—and you know that it's not from supplements—see your doctor to rule out any health problems.
MYTH: Drinking lots of water suppresses the appetite.
TRUTH: While being adequately hydrated helps your metabolism run at its optimal level, drinking vast quantities of water won't affect the amount you eat. Because water empties from the stomach very quickly, it has little effect on appetite, says Barbara Rolls, professor of nutritional sciences at Pennsylvania State University. A better way to feel sated with less, studies show, is to eat foods that have a high water content: fruits, vegetables, soups, and grains (see the chart at the end of this article).
MYTH: Bottled water is always better than tap water.
TRUTH: Although much ink has flowed on the pros and cons of tap versus bottled water, there is no simple answer. The government keeps tabs on the safety of tap water, but the water from your sink may have trace levels of contaminants, such as lead from old pipes.
To determine the health of your municipality's water supply, visit the Environmental Protection Agency's drinking water site (www.epa.gov/safewater/dwinfo). To find out if lead from old pipes is seeping into your taps, consider a home water test, such as Watersafe ($17 at www.watersafe testkits.com). If any contaminants show up, try using a filter appropriate for the type of contaminant, suggests Jeff Migdow, M.D., a holistic physician affiliated with Kripalu Center for Yoga & Health in Lenox, Massachusetts.
If you'd rather buy bottled, splurge on spring water from a reputable source. "Much of bottled water is simply tap water that's been filtered," says Migdow. Indeed, a 1999 report from the Natural Resources Defense Council cites government and industry findings that roughly 25 percent of bottled water is nothing but plain tap water. If you're curious about the source of your favorite brand of bottled water, go to www.nsf.org/consumer and click on "bottled water."
drink your food No more eight glasses a day: New research says you can get your water from food and even coffee.
SERVING SIZE AMT. OF WATER % BY VOL.
lettuce 1/2 cup 1.8 oz. 95%
broccoli 1/2 cup 2.7 oz. 91%
grapefruit 1/2 cup 3.4 oz. 91%
raw carrot 1 medium 2.1 oz. 87%
apple 1 medium 3.5 oz. 84%
spaghetti (cooked) 1 cup 3.3 oz. 66%
watermelon 1 cup 5.1 oz. 92%
skim milk 8 oz. 7.5 oz. 94%
coffee or tea 8 oz. 7.9 oz. 99.5%
Catherine Guthrie is a health writer and yoga instructor in Bloomington, Indiana.