💧 Hydration Guide 5 min read
How Much Water Should I Drink Per Day?
The popular "8 glasses a day" rule is a rough approximation — your actual needs depend on body weight, activity, climate, and diet. This guide explains the formula behind the number, gives you a weight-based reference table, and covers the situations where you need to drink significantly more.
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Water Intake Calculator →The baseline formula
A widely used clinical guideline — referenced by the European Food Safety Authority (EFSA) and used in sports nutrition — is 35 ml per kg of body weight per day for a sedentary adult in a temperate climate. This covers total fluid, most of which should come from plain water and non-caloric beverages.
Daily water target by body weight
Use the table below as a starting baseline. The values assume a sedentary to lightly active lifestyle in a moderate climate. Add the appropriate amount from the activity section below if you exercise.
| Body weight | Daily baseline (35 ml/kg) | Lightly active (+400 ml) | Moderately active (+700 ml) |
|---|---|---|---|
| 50 kg (110 lb) | 1.75 L | 2.15 L | 2.45 L |
| 60 kg (132 lb) | 2.10 L | 2.50 L | 2.80 L |
| 70 kg (154 lb) | 2.45 L | 2.85 L | 3.15 L |
| 80 kg (176 lb) | 2.80 L | 3.20 L | 3.50 L |
| 90 kg (198 lb) | 3.15 L | 3.55 L | 3.85 L |
| 100 kg (220 lb) | 3.50 L | 3.90 L | 4.20 L |
Adjusting for activity and environment
Several factors can substantially increase your fluid needs beyond the baseline:
| Situation | Additional fluid needed | Notes |
|---|---|---|
| Light exercise (<45 min) | +400–500 ml | Brisk walking, yoga, light cycling |
| Moderate exercise (45–90 min) | +600–800 ml | Running, gym sessions, team sports |
| Intense exercise (>90 min) | +1,000–1,500 ml | Marathon prep, endurance training; consider electrolytes |
| Hot weather (>28 °C / 82 °F) | +500–700 ml | Increases regardless of exercise |
| High-protein diet | +300–500 ml | More fluid required to process nitrogen waste |
| Illness with fever / vomiting | +500–1,000 ml | Replace lost fluids; consult a doctor if prolonged |
| Pregnancy | +300 ml above usual | EFSA recommendation |
| Breastfeeding | +700 ml above usual | EFSA recommendation |
Reading your urine colour
Urine colour is the most practical real-time hydration indicator available. Use this guide throughout the day rather than relying on thirst alone, which can lag significantly behind actual fluid needs.
| Colour | What it signals | Action |
|---|---|---|
| Colourless / very pale | Over-hydrated | Reduce intake slightly |
| Pale straw / light yellow | Well hydrated | Maintain current intake |
| Yellow | Adequately hydrated | Continue normally |
| Dark yellow / amber | Mildly dehydrated | Drink 1–2 glasses now |
| Orange / brown | Significantly dehydrated | Drink water promptly; consider medical advice if persistent |
What counts as fluid intake?
Total fluid intake includes more than just plain water. All of the following contribute to your daily tally:
- Plain water — always the best primary source
- Tea and coffee — despite mild diuretic effects, net fluid contribution is positive
- Milk and plant-based milks — also provide electrolytes and nutrients
- Herbal infusions — fully count toward total fluid
- Soups and broths — significant contribution, especially in winter
- Water-rich foods — cucumber (97%), lettuce (96%), watermelon (92%), strawberries (91%), yoghurt (88%) all contribute
Sugar-sweetened drinks, alcohol, and energy drinks count as fluid but come with drawbacks that generally make them poor choices as primary hydration sources.
Common questions
How much water should I drink per day?
A useful baseline is 35 ml per kg of body weight. A 70 kg adult would target roughly 2.45 litres, adjusted upward for exercise, hot weather, or a high-protein diet.
Does coffee count toward my daily water intake?
Yes. Despite mild diuretic properties, caffeinated drinks like coffee and tea still contribute net fluid to your daily total. They are not as efficient as plain water, but they do count.
Is clear urine a sign of good hydration?
Not necessarily. Consistently clear urine can mean you are over-hydrating. Pale straw-yellow is the practical target for most people during normal activity.
How much extra water should I drink when exercising?
Add roughly 500 ml for light sessions under 45 minutes, and 700–1,000 ml or more for intense or long workouts. In hot weather, increase further based on how heavily you sweat.
Can you drink too much water?
Yes. Drinking excessive amounts over a short period can cause hyponatraemia (dangerously low blood sodium). This is rare and generally only a risk for people drinking several litres in one sitting. For most healthy adults, the practical risk is over-hydrating — producing very clear urine — rather than any serious harm.
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