How much water do you really need?
A practical baseline for healthy adults is roughly 30–35 ml per kilogram of body weight per day — this calculator uses 33 ml/kg, then adds about 350 ml per 30 minutes of exercise and extra for hot climates. For a 65 kg person, that's a little over 2 litres on a normal day.
Around 20% of daily fluid typically comes from food (fruits, vegetables, dal, curd), and tea, coffee and milk all count toward intake — the idea that caffeinated drinks "don't count" is a myth at normal consumption levels.
Signs you're getting it right
- Urine colour is the best everyday indicator: pale straw yellow means well hydrated; dark yellow means drink more.
- Thirst is reliable for most healthy adults — but blunted in older age and during intense exercise, when drinking to a plan helps.
- Headaches, fatigue and poor concentration are common early signs of mild dehydration.
Can you drink too much?
Yes. Forcing several litres beyond thirst — especially during endurance exercise without electrolytes — can dangerously dilute blood sodium (hyponatremia). More is not better; matched-to-need is better. People with kidney or heart conditions may need fluid limits and should follow their doctor's guidance rather than any calculator.
Sources & references
- EFSA Panel on Dietetic Products. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459.
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. 2005.