Water

On average, per day, approximately 2400mL of water enters and leaves the body. [* (2400mL)(1fl oz/29.57mL)(1qt/32fl oz)(1gal/4qt)=.634 gallon, approximately 1/2 gal]

Water enters the body in three different ways: (1) the liquids we drink (1500mL) [*(1500mL)(.001L/1mL)(1pt/.4732L=3.17pt], (2) water in foods (700mL=1.479pt), and (3) water produced in cells as a by-produce of the reactions by which food is broken down (200mL=.423pt).

Water normally leaves the body by four mechanisms: (1) urine produced in the kidneys (1400mL=.370gal which is approximately 1/4 gal), (2) water in expired air from the lungs (350mL=.740pt), (3) persperation from the skin (450mL=.950pt), and (4) feces formed in the intestines (200mL=.423pt gal).

For a body to function normally, the total volume of water intering the body must equal the total volume of water leaving the body. Serious dehydration can occur in an adult if there is a 10% net loss in total body fluid, and a 20% loss of fluid can be fatal. An infant suffers dehydration with a 5-10% loss in body fluid.

[source: Chemical Principles by H. Stephen Stoker]