Daily Water Intake Calculator

How is daily water intake calculated?

Water needs aren't one fixed number; body weight, physical activity and climate are the three main drivers. This calculator uses a widely accepted practical formula:

Daily water (ml) = 33 × weight (kg) + exercise bonus + climate bonus

• Base: ~33 ml per kg — in line with the European Food Safety Authority (EFSA) adult guidance (~2 L/day total fluids for women, ~2.5 L for men).
• Exercise bonus: ~350 ml per 30 minutes of training. Sweat losses can reach 0.5–2 litres per hour depending on intensity.
• Climate bonus: +500 ml in hot, humid weather.

Worked example: 70 kg, 60 minutes of training, summer

33 × 70 + 700 + 500 = 3,510 ml ≈ 3.5 litres (~14 glasses)

The same person on a winter rest day needs only ~2.3 litres — so it makes sense to flex your target from day to day.

Water and training performance

Losing just 2% of your body weight in fluids measurably reduces endurance performance; focus and strength suffer too. A practical plan for training days:

• 400–600 ml two to three hours before training,
• 150–250 ml every 15–20 minutes during the session,
• ~500–700 ml afterwards for every 0.5 kg lost.

If you're losing weight, water also helps appetite control — 500 ml before a meal can reduce how much you eat. Plan the calorie side with the calorie calculator.

Easy ways to drink more

• Start the day with a glass of water; have one before every meal.
• Keep a visible bottle on your desk — seeing it triggers drinking.
• If plain water bores you, add lemon, cucumber or mint.
• Always pack water for workouts — walks included (walking for weight loss).

Not medical advice. If you have a heart, kidney or liver condition, plan your fluid intake with your doctor. Drinking too much too fast (more than ~1 litre per hour for extended periods) carries a risk of hyponatraemia.