How the Water Intake Calculator works
The calculator is based on the weight-based method recommended by the European Food Safety Authority (EFSA) and adjusted for activity level and climate.
Base intake: 35 ml/kg/day (men) or 31 ml/kg/day (women)
Total = Base × Activity multiplier × Climate multiplier
Total = Base × Activity multiplier × Climate multiplier
Activity multipliers
- Sedentary: ×1.0 — desk job, no deliberate exercise
- Lightly active: ×1.15 — light exercise 1–3 times per week
- Moderately active: ×1.3 — exercise 3–5 times per week
- Very active: ×1.45 — hard exercise 6–7 times per week
- Extremely active: ×1.6 — athlete or physical labour job
Official recommendations
- EFSA: 2.0 L/day for women, 2.5 L/day for men (total including food)
- US IOM: 2.7 L/day for women, 3.7 L/day for men (total including food)
- These are averages for sedentary adults — active people need significantly more
How to use your results
The result is your total daily fluid intake including water from food (which accounts for approximately 20% of total intake). The actual water to drink is 80% of the total shown.
Spread your intake throughout the day: approximately 35% in the morning, 40% in the afternoon, 25% in the evening. Avoid drinking large amounts just before bed.
The best indicator of adequate hydration is urine colour: pale yellow (like lemonade) means well hydrated. Dark yellow or amber means you need more water. Clear/colourless can indicate overhydration.
Frequently asked questions
How much water should I drink per day?
For most adults: 2.0–2.5 litres per day for women, 2.5–3.0 litres for men, including water from food. Active people and those in hot climates need more — up to 4–5 litres on intense training days.
Does the 8 glasses of water per day rule apply to everyone?
No — the '8×8 rule' (8 glasses of 8oz = 1.9 litres) is a rough guideline. Actual needs vary by body weight, activity, climate and diet. A 100kg athlete needs far more than a 55kg sedentary person.
Can I drink too much water?
Yes — hyponatraemia (water intoxication) can occur when drinking excessive water rapidly, diluting blood sodium. This is rare in healthy adults but can happen during endurance events. Drink to thirst, not to a fixed number.
Does coffee count toward daily water intake?
Yes — despite being a mild diuretic, coffee is net hydrating. Studies show coffee contributes to daily fluid intake. Tea, juice, and other beverages also count. However, alcohol is dehydrating and doesn't count.
How does activity affect water needs?
Exercise increases water needs significantly. During exercise, you lose 0.5–2 litres per hour through sweat. Weigh yourself before and after exercise: every kg lost = 1 litre of fluid to replace.
Does eating water-rich foods count?
Yes — approximately 20% of daily water intake comes from food. Fruits and vegetables are 80–95% water. Cucumber, watermelon, strawberries, lettuce, and celery are among the highest water-content foods.
How do I know if I'm dehydrated?
Early signs: dark urine, thirst, decreased urination, dry mouth. Moderate: headache, fatigue, reduced concentration. Severe: dizziness, rapid heartbeat, confusion. Thirst is already a sign of mild dehydration — drink before you feel thirsty.
Should I drink more water to lose weight?
Drinking water before meals reduces calorie intake by 13% in some studies. Replacing sugary drinks with water significantly reduces daily calorie intake. Water itself has zero calories and no direct fat-burning effect.