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Health & Wellbeing2 min check
Water Intake Calculator
Step 1 of 10%
How it works
A common rule of thumb is 30-35 ml per kg body weight. Add ~700 ml per hour of vigorous exercise. Multiply by ~1.2 in hot conditions.
Roughly 20% of fluid intake comes from food (fruits, vegetables, soups), so the drink target is the rest.
Worked example
70kg, 1 hour exercise, UK climate:
- Baseline: 70 × 0.033 = 2.31 L
- + Exercise: 0.7 L
- Total: ~3.0 L of fluid (about 12 glasses)
Who should use this
- •Active adults setting a hydration target
- •People recovering from illness or in hot weather
- •Anyone tracking general wellness
Common mistakes
- ×Drinking only when thirsty (older adults especially have a blunted thirst signal)
- ×Forgetting that tea/coffee count — caffeine's diuretic effect is mild at habitual intakes
- ×Over-drinking — hyponatraemia is rare but possible at extreme intakes (>1 L/hr)
- ×Counting alcohol as hydration (it's net dehydrating)
Frequently asked questions
Does coffee dehydrate me?▾
Habitual caffeine consumers tolerate it without significant fluid loss. Coffee net contributes to hydration.
Can I drink too much water?▾
Yes — hyponatraemia (low sodium) can occur if you drink several litres very quickly, especially during endurance events.
Does food count?▾
Yes — fruits, vegetables, soups and stews can provide ~20% of daily fluid.
How can I tell if I'm hydrated?▾
Urine colour. Pale straw = good. Dark yellow = drink more. Clear constantly may mean over-drinking.