How much water should I drink a day?

How it works

1. The National Academies set an Adequate Intake for total water, from drinks and food together, of about 2.7 litres a day for women and 3.7 litres for men.
2. They note that about 80% of that comes from drinks and about 20% from food.
3. The portion slider is our own arithmetic on those figures: if you are eating half your usual amount, you get roughly half the usual water from food, and drinks make up the difference. It is a rough estimate, not a clinical target.
4. For comparison, the European Food Safety Authority considers 2.0 litres a day adequate for women and 2.5 litres for men.

Before you use the number

• The prescribing information for semaglutide (Wegovy) and tirzepatide (Zepbound) warns of acute kidney injury in people who became dehydrated through nausea, vomiting or diarrhea. If you cannot keep fluids down, contact your prescriber.
• If a doctor has set you a fluid limit, for example for heart failure or kidney disease, follow that and not this.
• Needs go up in heat, with exercise, and when you are unwell.

This is general information, not medical advice, and it does not replace your prescriber or a dietitian who knows you.

Questions people ask

Sources

• National Academies: water Adequate Intake, 2.7 L and 3.7 L, about 80% from drinks
• EFSA: 2.0 L for women and 2.5 L for men (2010)
• Wegovy US prescribing information, section 5.5
• Zepbound US prescribing information, section 5.3

Figures checked against the sources above on 21 September 2026.