While there is no official recommendation for how many ounces of water a person should drink each day, the U.S. Department of Agriculture establishes Adequate Intake (AI) amounts to be used as guidelines. The AI for women ages 19 and above is 2.7 liters or about 91 ounces a day; for men ages 19 and above, 3.7 liters or about 125 ounces a day.