Water, which has been sloshing around the Earth for billions of years, is suddenly fashionable. No longer content to quench their thirst from the nearest tap, many Americans have taken to toting their water with them, buying a record 3.2 billion gallons of the bottled variety in 1998, about three times as much as a decade ago. While there's no evidence that bottled water is any better for people than the free-from-the-fountain kind, the liquid's newfound popularity represents a healthy trend.

　　Indeed, water is as vital to a good diet as low-fat foods, fruits, vegetables, and whole grains. Some 55 to 65 percent of a man's body and 50 to 60 percent of a woman's consists of water, which is necessary for the proper functioning of every organ, including the heart and brain. Without it, you can't digest food, regulate body temperature, or build new tissue.

How Much You Need

　　Most of us have heard from childhood that we need eight glasses of water each day. But this is an arbitrary figure, an average derived from studies that measure body composition and water loss. You may require somewhat more or less, depending on climate and the activities you pursue.

　　Any liquid that has water in it helps meet your daily goal. In addition to the water, milk, fruit juice, coffee, and tea you drink, your body extracts water from the food you eat. In fact, many fruits and vegetables are more than 90 percent water. Your body also produces water as a byproduct of metabolism. So don't be concerned if you fail to drink eight glasses of water a day. A simple way to see if you're taking in sufficient fluids is to check the color of your urine. If it's pale, you're getting enough fluids; if it's dark yellow, however, you're not.

　　Many people have also been led to believe that drinking coffee or tea will interfere with their ability to get as much water as they need. While it's true that the caffeine in coffee and tea is a diuretic, which tends to increase the output of urine, these beverages do contribute to your personal water supply. If you drink a cup of either one, you'll urinate away half of what you take in within a couple of hours; that may seem like a lot, but if you drink a glass of plain water, you'll urinate away 35 percent. The point is, you lose a significant amount of all the fluid you drink--which is why you have to keep replenishing it daily.

　　Unfortunately, thirst isn't a good indicator of when to drink water, especially when you're exercising. During vigorous physical activity, you may lose a significant amount of your fluid reserves before you're aware that you're thirsty. Only after you have dropped 2 percent of your body weight in fluid is your thirst mechanism triggered. (If you ignore that thirst and drop 4 percent, your muscles can lose their strength and endurance.) "Plan to drink a lot of water before you start to exercise," recommends Dorothy Diehl, Ph.D., an exercise physiologist at Plymouth State College, in Plymouth, New Hampshire. "Then take regular water breaks during a workout, whether you're thirsty or not."

Bottled Versus Plain

　　Do you need your water shipped in from France, or can you just turn on your kitchen tap and fill a glass? It makes little difference to your body. Bottled waters can come from wells, springs, and even public water supplies. Although the labels sometimes picture cool mountain glens, the water in the bottle may have come from a tap in a neighboring town. "Don't assume that drinking tap water will make you ill or that bottled water will help you remain healthy," says Diehl.

　　Since the Environmental Protection Agency strengthened the Safe Drinking Water Act in 1996, people who use municipal water can drink it with assurance. Water companies adhere to mandatory standards, and the water is tested regularly. If your water is provided by a municipal water company, your supplier must tell you within 24 hours if the water has become contaminated by something that can cause you to become ill and whether it must be boiled.

　　In addition, states compile information from individual water systems so that you can evaluate the overall quality of your local drinking water. Water companies are now required to distribute annual reports with information about where your drinking water comes from, the results of monitoring, and updates on health concerns associated with violations that occurred during the year. So here's to your health: Drink up!

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