Water makes up more than half of your body weight and is involved in almost everything your body does — from regulating temperature to transporting nutrients.
Yet there is a lot of confusion about how much you actually need to drink. Here is a simple, evidence-based guide.
What official guidelines say
| Source | Women | Men |
|---|---|---|
| European Food Safety Authority (2010) | 2.0 L/day | 2.5 L/day |
| US National Academies (2005) | 2.7 L/day | 3.7 L/day |
These figures include water from food, which usually provides around 20–30% of the total. Fruit, vegetables, soups and yogurt all contribute. So the amount you need to drink is lower than these totals.
Is “eight glasses a day” right?
Eight 250 ml glasses is 2 litres — a reasonable ballpark for many adults, but it is a rule of thumb rather than a scientific requirement. Larger, more active people or those in hot climates usually need more; smaller, less active people may need less.
A simple way to estimate your needs
Example: a 70 kg person who exercises for 30 minutes a day: 70 × 33 = 2,310 ml, plus about 360 ml for exercise ≈ 2.7 litres per day.
What counts towards your fluid intake?
- Water — the best everyday choice: no calories, no sugar.
- Milk and plant-based milks — also provide protein and other nutrients.
- Tea and coffee — count towards your intake for regular drinkers, despite caffeine’s mild diuretic effect.
- Sugary drinks and juice — hydrate, but add sugar and calories, so keep them limited.
How to tell if you are drinking enough
- Your urine is pale yellow for most of the day.
- You rarely feel very thirsty.
- You drink more when exercising, in hot weather, or when unwell with fever, vomiting or diarrhoea.
Can you drink too much water?
Rarely, yes. Drinking very large volumes in a short time — for example during long endurance events — can lower blood sodium levels (hyponatraemia), which can be dangerous. During long events, drink to thirst and consider drinks containing electrolytes.
Try the calculators
Put this guide into practice with a free estimate.
Frequently asked questions
How much water should I drink a day?
Many adults need roughly 1.5–3 litres of fluid from drinks per day, depending on body size, activity and climate. Official total-water guidelines, including food, are 2.0–3.7 litres.
Does coffee dehydrate you?
For people who drink it regularly, coffee contributes to daily fluid intake. Its mild diuretic effect does not outweigh the fluid it provides.
Should I drink water before meals?
Drinking water with or before meals is a healthy habit and may help some people feel fuller, but it is not a weight-loss method on its own.
Methods and sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal 2010;8(3):1459.
- National Academies — Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005)