Healthy adult kidneys are capable of processing 15 liters of water or almost 4 U.S. gallons, per day, if one drinks the water in small quantities spread throughout the entire day. It is not advisable, however, to drink 15 liters of water daily over a long period.
The United States Department of Agriculture, food and nutrition information center, in general recommends an average daily fluid intake, including liquids from foods and other beverages, of 2.7 liters or 91 ounces for women, and 3.7 liters or 125 ounces for men spread throughout the day.
It is important to realize that the center's recommendation varies more or less with body mass, activity level, heat, humidity, and health status.
In addition, the average healthy person should ingest no more than approximately 240 milliliters, or close to 8 ounces, in roughly an hour giving the body adequate time to absorb use and excrete the water effectively.
People with known health conditions, particularly conditions affecting water balance, should discuss hydration with a doctor specializing in their particular medical concern.