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, soups, yogurt), 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.
Practical guide for using this result
How to use the range
Start near the middle, then adjust for thirst, urine colour, heat and sweat while avoiding the idea that clear urine all day is always better.
Exercise hydration
For short sessions, normal meals and water are often enough. Longer hot sessions may need planned fluid and electrolytes.
Warning signs
Confusion, severe headache, vomiting, fainting or rapidly worsening weakness during exercise require urgent assessment.
How to use a daily fluid target
Fluid needs vary with heat, exercise, altitude, pregnancy, breastfeeding, diet and illness. Food also contributes water, so the result is a practical target rather than a strict prescription.
Spread intake through the day
Drink regularly with meals and between activities instead of trying to catch up all at once. Increase around exercise and hot conditions.
Use simple hydration checks
Thirst and pale-yellow urine are useful for many healthy adults, although supplements, medication and illness can change urine colour.
Avoid forced overdrinking
Excessive water in a short period can be dangerous. Kidney, heart or liver disease may require an individual fluid plan from a clinician.
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.