Water is your body’s most important nutrient, is involved in every bodily function. The human body has a significant amount of water in it. The amount of water depends on a person’s age, and the amount of fat that is stored in the body. Water Is In The Human Body for adults. An average fit adult woman generally has more fat tissue than does a man of similar fitness and age. On average an adult male may normally have around 60% water weight, a female may normally have between 56-58% water weight.