The human body is made primarily of water. The average range is 60 to 70 percent for adult males and females respectively; however, an infant’s body contains up to 75 percent. This percentage lowers with age. A bedridden elderly person or a dehydrated person could have as low as 50 percent water, and they are given intravenous fluids. To stay healthy, an adult is encouraged to drink at least eight full glasses of water a day.