Answer
A person typically gains and loses 2,500 mL of water per day.
Sources of water gain include metabolic water and performed water.
Water is lost as urine, fecal moisture, in expired breaths, sweat, and cutaneous transpiration.
Work Step by Step
Because a person is in a state of fluid balance, the amount of water a person gains is equal to the amount lost. This amount is 2.5 L of water per day.
About 200 mL/day of water is gained as a by-product of dehydration synthesis reactions and aerobic respiration (metabolic water). Another 2,300 mL/day of water is gained by eating and drinking (performed water).
Water is lost in:
Urine: 1,500 mL/day
Feces: 200 mL/day
Expired breath: 300 mL/day
Sweat: 100 mL/day
Cutaneous transpiration: 400 mL/day
The amounts lost can vary. Working in a hot environment can increase the water lost by sweating. Breathing in a cold environment increases water loss by breathing.
