How to use the Water Intake
- Enter your body weight.
- Add exercise duration and intensity.
- Adjust for hot or humid conditions and altitude.
- Subtract the contribution from food if you want a drinking-only target.
How the calculation works
A reasonable baseline is 30 to 35 ml per kg of body weight per day of total water, which for most adults lands between 2 and 3 litres. Exercise adds roughly 400 to 800 ml per hour depending on intensity and heat, and sweat rates vary enormously between individuals — weighing yourself before and after a session gives a far better personal figure than any formula, since each kilogram lost is about a litre of fluid.
Around 20% of total water intake comes from food, so a 2.7 litre total corresponds to roughly 2.2 litres of drinking. Thirst is a reliable guide for most healthy adults; urine colour, pale straw rather than dark yellow, is a practical check. Overdrinking is not harmless — endurance athletes who drink far beyond sweat losses can develop hyponatraemia, which is why plain volume targets should not override how you feel.
Baseline ≈ 30–35 ml per kg per day ; add 400–800 ml per hour of exercise ; food supplies ≈ 20% of totalSource: EFSA and US National Academies adequate intake values for total water; sweat replacement guidance per American College of Sports Medicine.
Worked example
A 74 kg person training for 70 minutes in warm conditions.
- Baseline = 74 × 33 ml = 2,442 ml.
- Exercise addition ≈ 70/60 × 650 = 758 ml.
- Total ≈ 3,200 ml.
- Less roughly 20% from food: about 2,560 ml to drink.
Around 3.2 litres of total water, of which roughly 2.6 litres comes from drinks — spread through the day rather than consumed in bulk.
Frequently asked questions
Do I really need eight glasses a day?+
No — that figure has no scientific origin. Needs vary with body size, activity and climate, and food already supplies about a fifth of your total.
Do tea and coffee count?+
Yes. The mild diuretic effect of moderate caffeine does not offset the fluid consumed, so caffeinated drinks contribute to daily intake.
How do I know if I am drinking enough?+
Pale straw urine and absence of persistent thirst are good practical indicators. For training, weigh before and after a session — each kilogram lost is about a litre of fluid.
Can you drink too much water?+
Yes. Drinking far beyond sweat losses, particularly during long endurance events, can dilute blood sodium dangerously. Drink to thirst and replace electrolytes on long efforts.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.