This image features a walking toddler with her muscles and fat revealed. The percentage of constant water in your body is related to the amount of fat and muscle you have; the more muscle you have, the more water. Babies' bodies are composed of a whopping 70% water. However, this high percentage is not due to muscle; rather, most of that water is to provide cushioning during the birthing process.
Water also plays an important role in our lives before we are even born. We begin life completely submerged. While in utero, a baby is protected 360 degrees around by fluid under pressure, which pillows her against bumps from the outside world and softens jolts and jostles. The life-giving environment of the womb is almost entirely water: the chemical composition of amniotic fluid is 98% to 99% water, varying slightly throughout stages of gestation. The baby not only floats in the sphere of protective fluid, but "breathes" it; every three hours, amniotic fluid is circulated as the baby swallows the fluid and releases it through urine.