How much water should I drink a day?
What the standard actually says
The figures come from the U.S. National Academies of Sciences, Engineering, and Medicine, reported by Mayo Clinic. The recommended adequate total water intake is about 3.7 L (~15.5 cups) per day for men and 2.7 L (~11.5 cups) per day for women.
A key detail is that these totals cover all water you take in — not just what you drink. They include water from food and from every beverage, including coffee, tea, milk, and juice, not only plain water.
These are population-level adequate intakes for generally healthy adults, meant to describe what a typical person needs, not a target you must hit exactly each day.
From total intake to what you drink
Because about 20% of daily water typically comes from food — think fruit, vegetables, soup, and other moisture-rich meals — the beverage share is smaller than the headline total.
Working the numbers: roughly 13 cups of fluids a day for men and about 9 cups for women, with the rest made up by food. That gap between total intake and drinking is why the drinking target sounds lower than the 15.5 and 11.5 cup figures.
You can run your own totals — and see the food-versus-beverage split — with the Water Intake Calculator.
What moves your needs up
The adequate intake figures describe a baseline. Several factors raise how much water the body needs above it.
Needs rise with exercise, heat, and altitude, all of which increase fluid loss. They also rise during pregnancy and breastfeeding, and during illness — for example when fever, vomiting, or diarrhea are present.
The more you sweat or lose fluid, the more the standard baseline understates your needs. These are directional factors the guidance flags, not fixed add-ons with a single universal number.
Where the '8 glasses a day' rule fits
The familiar '8x8' rule — eight 8-ounce glasses a day, about 1.9 L — is a simple, reasonable target. It is easy to remember and lands in a sensible range for many people.
It sits below the total-intake figures above largely because it counts only what you drink and does not include water from food. As a rough rule of thumb it works; as a precise personal requirement it is not what the National Academies figures are.
This is general information, not medical advice. Individual needs vary with health conditions and medications, so talk to a clinician about what is right for you.
Frequently asked questions
Does coffee or tea count toward my water intake?
Is 8 glasses of water a day enough?
How much of my daily water comes from food?
When do I need more water than the baseline?
Sources: Water: How much should you drink every day? — Mayo Clinic (U.S. National Academies).
Last reviewed July 4, 2026 · Editorial policy · This is general information, not financial advice.