Water is crucial to your health. It makes up, on average, 60 percent of your body weight. Every system in your body depends on water.
Lack of water can lead to dehydration, a condition that occurs when you don't have enough water in your body to carry on normal functions. Even mild dehydration - as little as a 1 percent to 2 percent loss of your body weight - can sap your energy and make you tired. Dehydration poses a particular health risk for the very young and the very old.