The human body is mostly water: about 55% to 75%, on average (and depending on how well hydrated you are). That’s about 10 to 12 gallons of water in your body!
Water makes up about 83% of blood, 73% of muscles, 25% of body fat, and 22% of bones.
The percentage of water in infants is much higher, typically around 75-78% water, dropping to 65% by one year of age. Body composition varies according to gender and fitness level because fatty tissue contains less water than lean tissue. The average adult male is about 60% water.