Final answer:
Total body water constitutes about 60-70% of an adult's body weight, being higher in infants and decreasing with age. It's distributed throughout the body's cells and tissues, with the brain and kidneys having the highest water content.
Step-by-step explanation:
Total body water is a significant percentage of a person's body weight. In adults, the total body water makes up about 60-70% of body weight. This water is distributed throughout the body in various compartments including both the intracellular fluid, accounting for 50% in case of lean persons, and the extracellular fluids, which in total represent about 20% of body weight. Infants have a higher percentage of body water at around 75%, which tends to decrease with age. Furthermore, certain organs, like the brain and kidneys, have higher water content, making up approximately 80-85% of their mass.
On top of being essential for internal processes such as digestion, circulation, and regulation of temperature, water participates in osmosis — the movement through semi-permeable membranes, balancing solute concentrations across cells. A healthy hydration level is crucial as the body loses water daily through urination, perspiration, and respiration, with recommendations to drink at least five or more 16-ounce glasses of water each day to replenish these losses.