Hydration tool
Water Intake Calculator
A friendly starting range for how much to drink in a day, based on the European Food Safety Authority's reference values. It is a rough guide, not a target to force down. Thirst and the colour of your wee are still the best day-to-day signals.
How this works
The starting point
EFSA's adequate intakes are about 2.0 litres of water a day for adult women and 2.5 litres for adult men, plus about 0.3 litres in pregnancy and 0.7 litres when breastfeeding. Those figures count water from everything, food included, in a mild climate with moderate activity.
Food counts too
Food usually provides around a fifth of daily water, so the drinks part is about 80 percent of the total. On a day when you fast for most of it, that food water mostly disappears, so the calculator counts the whole total as drinks.
Exercise and heat
Sweat rates vary enormously, from about 0.3 to more than 2 litres an hour depending on the person, the effort and the weather. The calculator adds a modest 0.4 to 0.8 litres per hour of exercise as a rough guide, and widens the top of the range on hot days. If you train hard or in heat, weighing yourself before and after a session is the most reliable way to learn your own sweat rate.
Do not overdo it
More is not always better. Drinking far more than your body needs, very quickly, can dilute the salt in your blood. If you have heart or kidney problems, or have been told to limit fluids, follow your doctor's advice rather than this range.
References
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific Opinion on Dietary Reference Values for water. EFSA Journal, 8(3):1459. Read the opinion
- Sawka, M.N. et al. (2007). American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377 to 390. Read the abstract
- Armstrong, L.E. & Johnson, E.C. (2018). Water Intake, Water Balance, and the Elusive Daily Water Requirement. Nutrients, 10(12):1928. Read the review
For healthy adults. This is general information, not medical advice.