ABSTRACT
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Water accounts for about 60% of body weight in an average human, varying mainly with degree of adiposity. As the percentage of body fat increases, the amount of body water decreases. Water is distributed in virtual compartments in the body, moving between compartments by osmosis or pumps. Total body water (TBW) is about 42 l in a 70-kg person, or 600 ml/kg. TBW is divided into intracellular fluids (two thirds TBW, 400 ml/kg) and extracellular fluids (one third TBW, 200 ml/kg). About 75% of the extracellular fluid is distributed interstitially between cells (150 ml/kg), and about 25% of extracellular fluid is found in the intravascular space (50 ml/kg).
