Did you know that when you're properly hydrated, about two-thirds of your body is water—muscle tissue is even higher, at around 70 percent, while fat is less.
Muscle powers your body and fat protects it. Put two and two together, and you may infer that water is vital to the things that make your body do stuff. When you don't drink enough water, your body declines into a state we call dehydration. Get too dehydrated, and your body will not function properly, which isn't too surprising when your body's low on such a vital nutrient.
You'll often hear claims that water helps chemical reactions, regulates your body temperature, and lubricates your joints, eyes, and spinal cord.
Sure, it does all of this stuff. In fact, since you're mostly made up of water, a case can be made that it does almost everything. Your body doesn't work, at all, without water. You can live days, weeks, and, sometimes, even months without food. But you can't live even a few days without water.
Water is the main component involved in mobilizing fat to be used as energy when we workout. A well-hydrated body has higher levels of oxygen in the bloodstream, translating into an increased ability to burn fat as fuel. The more efficiently you burn fat as fuel, the more effectively you exercise, leading to a better overall body composition.
How much water do I need?
It's said you need about 8 glasses of water a day. This will vary due to your activity level and environmental conditions. As a general rule, add a couple of glasses during the hot days of summer and the dry, cold nights of winter. During exercise, you may lose a quart an hour or more.
NOTE: While all liquids provide water, sugar, diuretics (caffeine, etc.), and carbonation reduce the hydration effect. Combining all three, as in soda, can reduce the hydration efficiency of the liquid to almost nil.