What percentage of body mass is water in humans?

In humans, water makes up about 60% of total body weight on average. This percentage varies by age, gender, and body composition infants have about 75%, adult men around 60%, and adult women about 50–55% due to higher fat content. Lean muscle tissue contains roughly 75% water, while fat holds only about 10%. Most body water is intracellular (inside cells), making up about two-thirds of the total. The rest is extracellular, found in blood plasma and interstitial fluids. Water enables nutrient transport, temperature regulation, and chemical reactions. Even a 2% drop in body water can cause dehydration symptoms like fatigue or reduced focus. Proper hydration keeps metabolism, circulation, and thermoregulation efficient. Thus, maintaining this internal balance is critical for health and survival.