How it works
Your body gets water from drinks and from food — fruit, vegetables, soup and rice all contain a lot of it. The European Food Safety Authority (EFSA) set adequate total water intakes for adults of 2.0 litres a day for women and 2.5 litres for men, from all sources. About 70–80% of that usually comes from drinks, so the calculator takes 80% as the drinking target and adds about half a litre for each hour of exercise.
drinks (L) = EFSA total × 0.8 + 0.5 × hours of exerciseMany people also use a weight-based rule of thumb of 30–35 mL per kg of body weight. The result shows that range too, so you can compare both.
Worked example. A man weighing 70 kg who exercises 1 hour a day: 2.5 × 0.8 + 0.5 = 2.5 L of drinks, about 10 glasses of 250 mL. The weight rule gives 70 × 0.03 to 70 × 0.035 = 2.1–2.45 L. A woman of 60 kg with no exercise: 2.0 × 0.8 = 1.6 L (weight rule 1.8–2.1 L).
When you need more
- Hot weather: in Gulf summers at 40 °C and above, sweat losses can add a litre or more a day, especially outdoors.
- Fever, vomiting or diarrhoea increase losses; oral rehydration solutions may be needed.
- Breastfeeding raises needs by about 700 mL a day (EFSA).
- Ramadan fasting: spread drinks between iftar and suhoor rather than drinking a large amount at once.
Signs you are drinking enough
Pale yellow urine and rarely feeling thirsty are good everyday signs. Drinking far more than you need is not better: very large amounts in a short time can be dangerous. People with kidney, heart or liver disease may have fluid limits set by their doctor — follow those instead.
Converting bottle sizes? The mL to oz converter helps. For your daily food energy, see the calorie calculator.