Many people have been taught to drink 64 oz. of water, or about eight cups, a day. The reality is that there is no hard and fast rule and each person's water needs are unique. They depend on how much you weigh, your diet and your activity level. Actively trying to lose weight further complicates this formula, because you may be exercising. Additionally, though there is no substitute for water, other fluids can contribute to your total daily requirements.
Water and Dieting
According to MayoClinic.com, even mild dehydration can sap you of energy and make you feel tired. This is, of course, not productive when you are trying to lose weight, because you may feel too unwell to exercise or you may attribute the unpleasant effects of dehydration to your diet and be tempted to quit. Water is central to all your body's functions, including digestion and metabolism. Water carries nutrients to your cells and flushes toxins from your body. Additionally, drinking water fights water retention, which may be stopping the scale from budging.
Total Amount
The Institute of Medicine recommends a total of nine cups of beverages for women and 13 cups a day for men. Liquids other than water, for example, milk or juice, count toward the requirement. According to MayoClinic.com, there are other standards you can follow. For example, most doctors recommend eight or nine cups of liquids a day for everyone. If you have a hard time tracking how much you are drinking, according to MayoClinic.com, you can rely on the standard 8 by 8 rule, which means you should drink eight cups of water eight times a day. When adding other beverages and food, many of which are largely composed of water -- like fruits -- you should be getting enough total liquid during the day.
Special Considerations
It may be counterintuitive, but not all liquids contribute to your hydration. In fact, some may actually dehydrate you. Alcohol, for example, causes dehydration, and a good rule of thumb is that you should drink a cup of water for every alcoholic beverage you consume. Caffeinated drinks, such as tea, soda or coffee, should not constitute a significant portion of your liquid intake. In very hot, humid weather or at altitudes greater than 8,200 feet, your body loses more water, so you have to drink more to replace it. It is not a good idea to rely solely on thirst to determine how much you drink, because by the time you are thirsty, you may already be slightly dehydrated.
Exercise
If you are trying to lose weight, you may be following an exercise regimen. During exercise, you lose water as you sweat, and it is very important to replace this lost water. Becoming dehydrated during exercise is dangerous because you may feel dizzy or lightheaded. In terms of motivation, if you do not stay well-hydrated during exercise you will simply feel plainly bad and be less likely to enjoy exercise and stick to your routine. According to the American College of Sports Medicine, drink two to three cups during the few hours before you begin exercising. Then, drink one-half to one cup of water every 15 to 20 minutes during your workout. If you are able to weigh yourself before and after working out, drink two to three cups of water afterwards for every pound you lost while exercising. During intense sessions, or sessions longer than an hour, drink a sports drink to replace the sodium and electrolytes you lose through sweating.
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