Water is lost from the body when a person urinates, defecates, sweats and breathes, according to the Centers for Disease Control and Prevention, or CDC. The average adult loses two to three liters of water every day, with one to two liters lost as urine, 100 to 200 milliliters lost as feces, 300 to 500 milliliters lost through breath and about one-half lifter lost through sweat, according to TheNutritionDr.
Water makes up about 60 percent of an individual's body weight, states the Mayo Clinic. To ensure proper hydration, adults need to replenish the same amount of water that is lost, explains TheNutritionDr. The typical recommendation of eight cups of water daily equals just under two liters.
The Mayo Clinic explains that there is no exact formula to determine how much water a person should drink daily. The CDC states that most people naturally drink enough water to replenish lost fluids during normal conditions, but under more extreme conditions people may need to increase their fluid intake. For example, if excess water is lost when a person experiences diarrhea, that person needs to take in additional fluid. The CDC explains that excess water may also be lost during strenuous activity or on a hot day.