A general rule of thumb for most adults is to drink eight 8-oz glasses of water every day to keep your body properly hydrated. That may seem like a lot, but it’s really not when you consider how much you lose every day in the course of normal metabolism.
For instance, you lose 3 to 4 liters (10 to 15 cups) of water each day through sweat, urine, bowel movements and respiration. Breathing alone accounts for 1 to 2 liters lost. Other factors can cause you to need even more water. Vigorous exercise, living in a hot climate, or a bout of diarrhea will mean your body requires more water for healthy functioning.