Why is Hydration Important?
Up to 60% of the human adult body is water. According to H.H. Mitchell, Journal of Biological Chemistry 158, the brain and heart are composed of 73% water, and the lungs are about 83% water. The skin contains 64% water, muscles and kidneys are 79%, and even the bones are watery: 31%.
How much water should you drink a day?
The old rule of "8 glasses a day" is a good baseline, but true water needs depend on your body weight and how much you sweat (activity level). For example, a 90kg athlete needs significantly more water than a 50kg office worker.