| Water Facts Chester J. Zelasko, Ph.D. 
| | The news media sometimes question things that most of us take for granted--for example, the age-old advice that you should drink eight 8-ounce glasses of water every day. ABC News wanted to know where that recommendation came from and sought to find it. The problem was they couldn't really pin it down. They asked scientists, nutritionists, government agencies, and historians. No one could cite even a single study that establishes that requirement. While there are no individual studies that we could find either, here are some interesting facts about water from basic physiology textbooks:  | The human body is about 40-60% water depending on fat mass. Why the difference? Because muscle tissue is almost 75% water while fat contains only 50% water. The more body fat, the lower the percentage--yet another reason to reduce body fat. | | We think of the bones as solid, but did you know that bones are over 30% water? So consider this: we always think in terms of calcium and magnesium for healthy bones, but adequate water intake is important as well. | | The brain is about 77% water. Even a small decrease in water content can mean it doesn't operate effectively, and that can result in fatigue, memory loss, and confusion. Often what we think is senility is just dehydration--serious, but easy to fix. | | Glycogen is the storage form of glucose in the body. The brain and muscles prefer glucose over any other source of fuel, but in order to store one gram of glycogen, your body needs 2-3 grams of water. This is another way inadequate water intake can lead to fatigue. | | On average every day, a 150-pound person will lose 1-1.5 liters of water in the urine, almost a liter of water through the skin (without exercise), about 0.4 liters through the lungs, and 0.1-0.2 liters through the feces. Added together, that works out to be 2.5-3.0 liters of water per day--without any exercise. That's about 100 ounces of water lost per day. Work in the yard on a hot day, and you lose much more. That's why we recommend an extra 4 ounces of water every 15 minutes when you're working or exercising in the heat. Kids playing outside need extra water, too--about 4 ounces every half hour. | While there are no definitive studies that result in a precise recommendation, these numbers indicate that the recommendation is about right. At BLI, we've updated that to reflect body size and recommend one-half your body weight in ounces of water per day. Of course, you get some water from the food you eat, especially fruits and vegetables, but given that most Americans eat less than four servings of fruits and vegetables per day, most of us aren't getting much water there either. Drinking water is the best way to stay hydrated, but weak tea and flavored water work, too. Caffeine-free drinks are better than caffeinated drinks because caffeine acts as a diuretic, which can make the problem worse. Speaking of diuretics, people who take a diuretic to lower their blood pressure are at increased risk of dehydration. They must be sure to drink the recommended amount of water every day. So keep drinking that water for optimal health. While you're at it, drink filtered water that removes the contaminants from municipal water supplies. Remember--if you don't use a water filter, you are the water filter. | |
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