For most adults, body weight is about 60 to 70 percent water. That equals roughly 10 to 12 gallons (38 to 46 L). Fat tissue is about 20 to 35 percent water whereas muscle tissue is about 75 percent water. Therefore, the total percentage of body weight from water depends on the ratio of fat to lean body tissue. People who have a higher percentage of lean tissue have a higher percentage of water weight. Men typically have a higher percentage of lean tissue and, thereby, a higher percentage of water weight than women. Younger people usually have a higher percentage of lean tissue and water weight than older people.