How Much Water Do You Actually Need?
The popular "8 glasses a day" rule is a rough estimate. Your actual needs depend on your weight, activity level, climate, and overall health. Drinking too little leads to dehydration; drinking excessively can dilute electrolytes (hyponatraemia).
The Weight-Based Formula
Base intake = body weight (kg) × 35 mL
OR body weight (lb) × 0.5 fl ozAdjustments
- Exercise: Add 500–1,000 mL per hour of moderate activity
- Hot/humid climate: Add 500–1,000 mL/day
- Pregnancy: Add ~300 mL/day
- Breastfeeding: Add ~700 mL/day
- High-altitude: Add 500 mL/day (increased respiration loss)
Quick Reference by Weight
- 60 kg → ~2.1 L/day
- 75 kg → ~2.6 L/day
- 90 kg → ~3.2 L/day
- 100 kg → ~3.5 L/day
Signs of Dehydration
Dark yellow urine, fatigue, headaches, and reduced concentration are early signs. Pale yellow urine indicates good hydration. Clear urine may indicate over-hydration.
Note: food contributes roughly 20% of daily water intake — fruits, vegetables, and soups count towards your total.
Get your personalised water target: Free Water Intake Calculator