Where the numbers come from
The National Academies of Sciences, Engineering, and Medicine set an adequate intake of total water, from all drinks and food, of about 3.7 liters (125 oz) a day for men and 2.7 liters (91 oz) for women. Food usually supplies about 20%, so drinks make up the rest: roughly 13 cups for men and 9 cups for women.
Adjustments
- Exercise: a common rule of thumb is about 12 ounces for every 30 minutes, more if you sweat heavily.
- Heat: hot or humid weather raises needs; the calculator adds about half a liter.
- Pregnancy and breastfeeding: total water needs rise to about 3.0 and 3.8 liters a day.
Signs you're well hydrated
Pale yellow urine and rarely feeling thirsty are good signs. All drinks count, including coffee and tea, as do water-rich foods like fruit and soup.
Frequently asked questions
Is 8 glasses a day right?
Eight 8-ounce glasses (64 oz) is a simple guide but isn't based on a specific study. Many adults need a bit more from all drinks, especially men and active people.
Can you drink too much water?
Yes. Drinking very large amounts quickly, especially during long endurance events, can lower blood sodium to dangerous levels.