How much water should I drink a day?
October 6, 2026 · 2 min read
The US National Academies put adequate total water intake at about 2.7 liters (91 oz) a day for women and 3.7 liters (125 oz) for men. European guidance (EFSA) is lower, at 2.0 and 2.5 liters. Both figures include water from all drinks and from food, not just the glasses you pour. In practice, about 1.5–2.5 liters of drinks a day covers most adults.
Water needs by body weight
A widely used rough estimate is 30–35 ml per kilogram of body weight (about half an ounce per pound):
| Body weight | Total fluid per day |
|---|---|
| 50 kg (110 lb) | 1.5–1.75 liters |
| 60 kg (132 lb) | 1.8–2.1 liters |
| 70 kg (154 lb) | 2.1–2.45 liters |
| 80 kg (176 lb) | 2.4–2.8 liters |
| 90 kg (198 lb) | 2.7–3.15 liters |
Treat this as a starting point, not a rule.
When you need more
- When you exercise. You need to replace what you sweat out. Half a liter to a liter extra for an hour of hard training is a reasonable estimate.
- In hot weather. Needs rise noticeably in summer.
- When you are ill. Fever, diarrhea and vomiting speed up fluid loss.
- During pregnancy and breastfeeding. Needs go up; discuss the amount with your doctor.
Is "8 glasses a day" right?
Eight glasses is roughly 1.9 liters (64 oz) and a sensible target for most people, but it is not a scientific requirement. Your needs change with your weight, activity and the weather. Tea and coffee count toward your intake; in moderate amounts the caffeine does not cause a net fluid loss.
How to tell if you are drinking enough
The most practical sign is urine color: pale straw means you are well hydrated, dark yellow means you should drink more. Thirst, headache, tiredness and a dry mouth are signals too.
Does water help you lose weight?
Water does not burn fat on its own, but it helps indirectly:
- Replacing sugary drinks with water removes hundreds of calories a day.
- A glass or two before a meal helps some people eat less.
- Thirst is sometimes mistaken for hunger, so drinking first can cut unnecessary snacking.
The deciding factor is still your calorie deficit.
Can you drink too much?
It is rare in healthy people, but drinking several liters in a short time can lower blood sodium to a dangerous level. Drinking when thirsty and spreading it through the day is enough. If you have a kidney or heart condition, your doctor should set your fluid intake.
Tracking your water
The usual reason people forget to drink is that they do not notice. In Cal Crew you log water in one tap and see how far you are from your daily goal. You can also compete with friends on water. We wrote separately about why tracking together works.