What percent of an adult’s total body weight is water?

• A. 40-50%
• B. 50-60%
• C. 60-70%
• D. 70-80%

Answer: (B)

Total body water as a portion of body weight is a key physiological measure. In adults, water makes up about half to a bit more than half of body weight, because tissues contain varying amounts of water and the body maintains distinct intracellular and extracellular fluid spaces. On average, males are around 60% water and females about 50-55% due to differences in body composition, especially fat content. So, the range around 50-60% best reflects the typical adult. Infants have a higher proportion of water, while older adults tend to have less, due to changes in lean mass and fat. For practical grounding, a 70 kg person would have roughly 35-42 liters of water, depending on sex and body composition.