How Much Water Should You Drink a Day When You Train?
The UK’s healthy eating guidance suggests 6 to 8 glasses of fluid a day, and the NHS notes you need more when you are active or it is hot. Water, lower-fat milk and sugar-free drinks, tea and coffee included, all count. On a training day, add a few hundred millilitres around the session and more if you sweat heavily. The simplest daily check is your urine: pale straw is about right, dark yellow means drink more. There is no need to force litres down, and drinking far beyond thirst carries its own risks. The rest of this post covers timing, how to judge your sweat losses and when plain water is not quite enough.
Where the 6 to 8 glasses figure comes from
The figure sits in the Eatwell Guide, the government’s model of a balanced diet, and the NHS repeats it in its advice on water, drinks and your health. It is a sensible baseline for an ordinary day, not a precise prescription. Two points are often missed:
- It is fluid, not just water. Tea and coffee count. So does milk. The old idea that caffeinated drinks dehydrate you overall does not hold for normal amounts in people used to them.
- Food contributes too. Fruit, vegetables, soups and yoghurt all carry water. Someone eating plenty of fresh food takes in a fair share of fluid at meals.
Your real need depends on body size, activity, room temperature and how much you sweat. A large man training hard in a warm room needs more than a smaller person on a desk day. That is why a single number is less useful than a few checks you can do yourself.
Three ways to judge your own hydration
- Urine colour. Pale straw through the day is the target. Very dark means drink more. Completely clear, all day, often means you are drinking more than you need. Some vitamin supplements turn urine bright yellow, so allow for that.
- Thirst. For healthy adults on an ordinary day, thirst is a reasonable guide. Older adults can feel thirst less, so a routine helps.
- The weigh-in test for heavy sweaters. Weigh yourself in minimal clothing before and after a typical session. Each kilogram lost is roughly a litre of fluid. If you regularly lose more than a small amount, drink more during and after.
Water around a training session
A simple plan that suits most people doing an hour of strength training:
| When | What to do |
|---|---|
| Through the day before | Drink normally. Aim to arrive with pale urine, not a full bladder. |
| 1 to 2 hours before | A glass or two of water with your pre-training snack or meal. |
| During the session | Sips between sets, to thirst. Bring a bottle of about 500ml to 750ml. |
| After | Drink with your next meal. If you sweated heavily, a bit more than you lost. |
Early morning sessions are the common weak spot. You have gone eight hours without a drink, and many people go straight from bed to the barbell with an espresso. A glass of water as soon as you get up, before the coffee, makes the first ten minutes noticeably easier for most clients. Our post on what to eat before a workout covers the food side of that window, and coffee before training covers the caffeine.
Signs you are under-hydrated during training
- Headache that builds through the session.
- Light-headedness when standing up from the bench or after a set.
- Unusual fatigue early in the session, before the hard work.
- Dark urine afterwards, or very little of it.
- Cramping, though cramp has several possible causes and is not always about fluid.
None of these is unique to dehydration. Poor sleep, too little food and hard training all produce similar symptoms. If they keep happening despite drinking well, look at the rest of the picture.
Can you drink too much?
Yes. Drinking very large volumes of plain water in a short time, especially during long endurance events, can dilute the sodium in your blood. This condition, hyponatraemia, can be serious. It is rare in an hour of gym training, but the principle matters: more is not always better. Drinking to thirst, with a sensible routine around sessions, protects against both extremes. Gallon-a-day challenges add nothing to your training and send you to the toilet every 40 minutes.
Do you need electrolyte or sports drinks?
For a typical hour of strength training, no. Water and your normal meals replace what you lose. Electrolyte drinks start to make sense when:
- You train for longer than about an hour, particularly in heat.
- You are a heavy, salty sweater (white marks on dark kit are a clue).
- You are doing two sessions in a day.
- You have been ill with vomiting or diarrhoea, where oral rehydration salts from a pharmacy are the right tool.
Many sports drinks contain a fair amount of sugar. That is useful in a long endurance event and unnecessary for most people at a desk all day. Read the label.
Water and the scales
Hydration shifts body weight from one day to the next, sometimes by a kilogram or more. A salty meal, a new training block or a long flight can all make you hold more water. It is not fat, and it passes. If you are tracking weight, use a weekly average. Our post on water weight fluctuations explains why the scales sometimes rise after a good week. Hydration can also affect body composition readings, so we ask clients to keep their routine consistent before an InBody scan: similar time of day, similar drinks, no session just before.
A daily routine that covers it
- A glass of water on waking.
- A drink with every meal.
- A bottle on your desk that you refill twice.
- A bottle in your gym bag, every session.
- Extra on hot days, travel days and after alcohol.
Check with your GP first if you have a heart, kidney or liver condition, or take medication such as diuretics, as you may have been given specific fluid guidance that overrides general advice.
In the studio
Hydration is one of the small details we keep an eye on in private sessions, alongside sleep, food and how you arrive on the day. It is rarely the whole answer, but it is an easy one to fix. If you would like a coach who looks at the full picture, read more about personal training at The Highgate House.
Questions we get asked
Does coffee count towards my water intake?
Yes. The NHS counts tea and coffee as fluid. Keep an eye on total caffeine, especially later in the day.
Should I drink water during a weights session?
Yes, sips between sets to thirst. You do not need to finish a set volume.
Will drinking more water help me lose fat?
Not directly. It can help with appetite if you often mistake thirst for hunger, and it replaces sugary drinks, which helps.
Is sparkling water as good as still?
For hydration, yes. Some people find it fills them up or causes bloating during training, so still is usually easier in the session itself.
For coaching that takes in these details, see 1-1 training in Highgate.
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