Hydration and Training
How much you need, what counts, and the one check that beats every rule of thumb. Most people are neither as dehydrated nor as at risk as the marketing suggests.
Last updated: 1 July 2026
Overview
Hydration is the fitness topic with the widest gap between how much it is sold and how much it matters.
You do need enough fluid, and being meaningfully dehydrated does hurt performance. You almost certainly do not need a gallon jug, an electrolyte sachet in every bottle, or to be sipping continuously through a 45 minute session.
Quick Answer
NHS guidance is to aim for 6 to 8 cups or glasses of fluid a day, increased in hot weather, during illness, or when exercising heavily. Water, lower-fat milk and lower-sugar drinks including tea and coffee all count towards it.
Key Points
- 6 to 8 glasses a day is the general guide, not a training-specific target.
- Tea and coffee count. They do not cancel themselves out.
- Pale yellow urine is a better check than any fixed number.
- Thirst is a reasonable signal for most people in most conditions.
- Electrolytes matter for long, hot, sweaty sessions, not for an hour indoors.
How much
NHS guidance is 6 to 8 cups or glasses of fluid a day, and it is explicit that this is a guide rather than a rule. It says the amount should go up if you are pregnant or breastfeeding, in a hot environment, exercising a lot, or ill.
Training adds to that, but not by a fixed amount. How much you need depends on how much you sweat, which depends on intensity, temperature, humidity, clothing and you.
| Situation | Rough extra |
|---|---|
| 45 to 60 min indoors, moderate | 500ml to 1 litre |
| Hard session, warm gym | 1 to 1.5 litres |
| Long outdoor session in heat | More, and with sodium |
What counts
More than people assume. NHS guidance counts water, lower-fat milk, and lower-sugar drinks including tea and coffee towards your daily intake.
The old claim that coffee dehydrates you does not hold at normal intakes. It has a mild diuretic effect, and the fluid in the cup more than covers it. A cup of tea is a cup of fluid.
Food contributes too. Fruit, vegetables, soup, yoghurt and rice all carry water that never shows up in anybody's bottle count.
The check that actually works
NHS guidance is to drink enough that your urine is a clear pale yellow.
That single check beats every fixed target, because it responds to your sweat rate, the weather and what you have eaten, none of which a number on a bottle knows about.
| Colour | Reading |
|---|---|
| Clear, almost colourless | Slightly more than you need |
| Pale yellow | About right |
| Darker yellow | Drink more |
| Amber or brown | Drink more, and see a doctor if it persists |
One caveat: B vitamins in a multivitamin turn urine bright yellow regardless of hydration, so the check is unreliable for a few hours after taking one.
What dehydration does to training
Meaningful dehydration reduces performance, and endurance work suffers before strength work does. Perceived effort rises, heart rate rises at a given pace, and heat tolerance drops.
The practical point is the word meaningful. Turning up slightly under-topped-up is not the reason a set felt hard. Sleep, food and how close to failure the previous set was are all larger factors.
Electrolytes
Sweat contains sodium, and long or hot sessions can lose enough to be worth replacing. Most gym training is neither.
| When electrolytes are worth it | When they are not |
|---|---|
| Over 90 minutes of hard sweating | A 45 minute session indoors |
| Training in real heat | Normal room temperature |
| A heavy, salty sweater over long sessions | Sedentary days |
| Endurance events | Replacing plain water generally |
For everything in the right-hand column, the sodium in a normal diet covers it.
Can you drink too much
Yes, and it is more dangerous than mild dehydration, though it is rare. Drinking far more water than you lose can dilute blood sodium, a condition called hyponatraemia, which in severe cases is a medical emergency.
It usually happens in endurance events where people drink heavily over hours while losing sodium in sweat. It is not a risk from ordinary sensible drinking.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Chasing a fixed litre target | Ignores your sweat rate and the weather | Use urine colour |
| Discounting tea and coffee | They count, per NHS guidance | Include them |
| Electrolytes in every bottle | Unnecessary sodium and expense | Save them for long, hot sessions |
| Drinking a litre right before training | Sits in the stomach | Spread it across the day |
| Blaming a bad session on hydration | Usually sleep, food or fatigue | Check those first |
Frequently Asked Questions
How much water should I drink a day?
NHS guidance is 6 to 8 cups or glasses of fluid a day, more if you are exercising heavily, in heat, or unwell. Training on top of that is usually another half to one and a half litres.
Does coffee count towards my fluid intake?
Yes. NHS guidance counts tea and coffee towards daily fluid intake.
Do I need electrolyte drinks?
For most gym sessions, no. They earn their place in long, hot, heavily sweating sessions and endurance events.
How do I know if I am dehydrated?
Urine that is darker than a pale yellow is the simplest signal, alongside thirst, headache and unusual fatigue.
Sources
NHS guidance on water, drinks and hydration - https://www.nhs.uk/live-well/eat-well/food-guidelines-and-food-labels/water-drinks-nutrition/
NHS eatwell guide - https://www.nhs.uk/live-well/eat-well/
American College of Sports Medicine - https://acsm.org/