Recommended water intake is 0.5 to 1 ounce of water per pound of body weight. This range accounts for a person’s size, and daily water intake should be adjusted within the range based on activity levels and climate, according to WebMD.
As a substitute for calculating water intake, the Institute of Medicine recommends an adequate intake of 13 cups of total fluids a day for an average man and 9 cups a day for an average woman, reports Mayo Clinic. Total fluids are a combination of fluids contained in foods and fluids obtained from drinking water and other beverages. About 20 percent of water intake comes from food. Physical exercise, hot climates, and acute and chronic illnesses cause excess fluid loss and increase daily fluid needs.