Nutrition
Hydration and performance: how much water you actually need
Losing 2% of bodyweight in sweat already hurts performance. Here is how much to drink, when, and with which electrolytes.
Dehydration is one of the few variables that degrades everything at once: strength, endurance, focus and perceived effort. Losing just 2% of bodyweight in sweat — 1.4 kg in a 70 kg person — is enough to feel the drop.
How much to drink each day
| Situation | Daily target | Notes |
|---|---|---|
| Sedentary, temperate climate | 30-35 ml/kg | ≈ 2.1-2.4 l for 70 kg |
| 1 hour of training | +500-700 ml | Split before and during |
| Heat or heavy sweating | +1-1.5 l | Add sodium |
| Long cardio (>90 min) | 400-800 ml/h | With electrolytes and some glucose |
How to tell if you are on track
- Urine colour: pale yellow is fine; dark amber signals a deficit.
- Bodyweight before and after training: each kilo lost equals a litre to replace.
- Persistent thirst, dry mouth and cramps: late signals, do not wait for them.
The 1.5 litre rule
For every kilo lost during a session, drink 1.5 litres over the following hours. The extra covers what you lose through urine while rehydrating.
Electrolytes: when they matter
Plain water is enough for sessions under 60-75 minutes in a temperate climate. Beyond that, or if you sweat heavily and see white salt marks on your kit, add 300-700 mg of sodium per litre. Potassium, magnesium and calcium are usually well covered by a normal diet.
Bottles and salts: simple works
A 1-litre bottle with volume markings and a tub of rehydration salts cover 95% of cases. Sugary commercial sports drinks rarely add anything if you are not competing.
See recommended bottles and electrolytes
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Talk to a professional
Drinking very large volumes of plain water during long events can cause hyponatremia, a serious condition. If you take diuretics or have heart or kidney failure, discuss your fluid plan with your doctor.
Frequently asked questions
- Does coffee dehydrate you?
- Not meaningfully at normal doses: the fluid in coffee counts towards your daily intake.
- Should I drink during weight training?
- Yes, small sips between sets. Around 300-500 ml across a one-hour session is enough.
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