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Hydration and exercise: how much should you drink to train?

We talk a lot about training and nutrition, rarely about water. Yet hydration is one of the simplest and most overlooked levers of performance. Just a few percent of dehydration is enough to make a session harder, ramp up fatigue and blur your focus. Conversely, drinking at the right time and in the right amount lets you hold intensity, recover better and feel stronger from start to finish. In this guide I'll give you clear markers: how much to drink before, during and after exercise, how to spot dehydration, and when electrolytes are genuinely worth it.

By Kael Martinez, certified personal trainer · 10 years of experience · Published June 21, 2026 · 10 min read

Why hydration changes everything

Your body is roughly 60% water. It's involved in almost everything that matters during exercise: transporting oxygen and nutrients, regulating temperature through sweat, lubricating the joints, muscle contraction. When water levels drop, these functions run less well, and you feel it fast in the quality of your session.

Performance dips before you notice

It's generally accepted that a water loss of around 2% of body weight already starts to impair performance: endurance collapses earlier, strength dips slightly, perceived effort climbs. For a 70 kg person, that's just over a litre of sweat, a volume easily reached in an intense session or hot weather. In other words, dehydration weighs on your results well before it becomes a real discomfort.

Thermoregulation, the main water expense

When you push hard, your muscles produce heat. To avoid overheating, your body sweats and evaporation cools you down. It's effective, but it uses water, sometimes a lot. The hotter and more humid it is, the more you sweat, and the greater the need to compensate. In Geneva, a session in mid-summer or in a poorly ventilated gym can cost noticeably more fluid than an equivalent winter session.

Recovery and focus depend on it too

Water doesn't only serve the session: it supports the recovery that follows, the delivery of nutrients to your muscles and the clearance of the by-products of effort. A mild dehydration sustained day after day often shows up as diffuse fatigue, headaches and dwindling focus. Hydrating well is a quiet but real pillar of good recovery, just like sleep.

How much to drink, and when: the real markers

There's no magic number that works for everyone: your needs depend on your weight, intensity, duration and heat. Even so, here are simple reference ranges to remember, to be adjusted according to your thirst and how much you sweat.

Timing Indicative amount Why
Across the day (baseline) 1.5 – 2 L Cover background needs, outside exercise
2 to 3 h before the session 400 – 600 ml Start well hydrated without feeling weighed down
15 min before 150 – 250 ml Final top-up, light sips
During (effort > 1 h or heat) 150 – 250 ml / 15-20 min Limit losses without overloading the stomach
After the session 500 ml – 1 L Replace what was lost in sweat

The best everyday indicator remains the colour of your urine: pale yellow signals good hydration, dark yellow a shortfall to make up. No need to force litres down at once: spread your intake across the day, in small regular amounts. If you want to connect these markers to the real intensity of your sessions, I cover it in how many calories a workout really burns.

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Before, during, after: the right timing

When you drink matters almost as much as how much. Spreading your intake well around the session lets you arrive ready, hold intensity and recover better afterwards.

Before: arrive already hydrated

Hydration is prepared in advance, not at the last sip on the doorstep. Drink regularly in the hours beforehand, then a light final top-up just before you start. The goal is to arrive with decent reserves, without a heavy stomach or having to interrupt the session for the toilet. If you train early in the morning, rehydrate as soon as you wake up, because the night dries you out.

During: small sips

For a short, moderate session, a few sips are enough if you started well. As soon as the effort goes past an hour, turns intense or takes place in hot weather, drink small amounts regularly rather than all at once: your stomach copes better and you avoid that bloated feeling. The classic mistake is waiting until you're truly thirsty, when thirst already lags slightly behind the real need.

After: replace and recover

Once the session is over, the goal is to replace what you lost. A good marker is to drink gradually over the following hours until your urine runs clear again. If you can weigh yourself before and after a big session, each half-kilo lost roughly corresponds to half a litre to replace. This rehydration fits into a wider recovery, where nutrition also plays a key role, as I explain on the muscle soreness and recovery side.

Water, electrolytes or a sports drink?

The sports-drink aisles make it feel like you need a specific product for every session. In reality, most of the time, water is enough. Here's how to decide without breaking the bank or swallowing pointless sugar.

For the vast majority of sessions: water

A strength, conditioning or cardio session under an hour doesn't warrant a special drink: plain water, at room temperature or cool, does the job perfectly. Sugary drinks mainly add liquid calories you don't need if your goal is weight loss. Save the sports products for the situations that truly call for them.

When electrolytes become useful

On long efforts (beyond 60 to 90 minutes), very intense ones, those repeated through the day or in hot weather, you lose not only water but also sodium through sweat. There, a drink containing electrolytes, and perhaps a little carbohydrate, helps maintain performance and rehydrate better. Plain water with a pinch of salt and a splash of juice often covers the need, without an expensive product. It's typically relevant during long-distance race preparation.

Coffee, tea and other drinks

Coffee and tea count towards your fluid intake: their diuretic effect stays modest at usual amounts. Alcohol, on the other hand, dehydrates and harms recovery, so avoid it around training. And beware of too much caffeine right before an intense session: it can heighten the feeling of a racing heart, especially if you're already slightly dehydrated.

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The most common hydration mistakes

Over the years, I keep seeing the same traps come back. Fixing them costs nothing and immediately changes how training feels.

Waiting until you're thirsty

Thirst is a useful signal, but a slightly late one: by the time it really kicks in, part of the deficit is already there. Rather than reacting to thirst, build the habit of drinking regularly across the day and around your sessions. This anticipation reflex is one of the most rewarding, especially on hot days when losses are fast.

Drinking it all at once

Swallowing half a litre right before or during exercise exposes you to digestive discomfort and an urgent need for the toilet. The body absorbs small amounts better. Regular sips beat one big glass at a time, before and during the session alike.

Underestimating heat and the gym

An overheated gym, an intense group class or an outdoor session in the Geneva summer sharply increase losses. Many keep the same habits as in winter and end up dehydrated without understanding why the session felt so hard. Adapt your intake to the weather and the venue's atmosphere, not just the displayed duration.

Confusing hydration with sugary drinks

Sodas, juices and energy drinks are not hydration tools: they mainly add sugar and, for some, caffeine. Hydrating with these drinks often sabotages a getting-back-in-shape or weight-loss goal. Water remains the reference, simple and free.

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Frequently asked questions

How much water should you drink per day when you exercise?

As a baseline, aim for about 1.5 to 2 litres of fluids a day, then add what you lose during exercise. A one-hour session can cost between 0.5 and 1.5 litres of sweat depending on intensity and heat, to replace on top. Needs vary with your weight, the temperature and how much you sweat: urine colour, ideally pale yellow, remains the simplest day-to-day marker.

Should you drink during a workout?

For a session under an hour at moderate intensity, a few sips are enough if you started well hydrated. Beyond an hour, in hot conditions or when you sweat heavily, drink regularly in small amounts, roughly 150 to 250 ml every 15 to 20 minutes, rather than all at once. The idea is to limit losses without overloading the stomach.

How do I know if I'm dehydrated?

The first signs are thirst, a dry mouth, dark and scant urine, and a drop in energy and focus. During exercise, creeping dehydration often shows up as early fatigue, a higher-than-usual heart rate and the feeling that everything gets harder. Thirst lags slightly behind the real need, so it's better to anticipate.

Are electrolyte drinks useful for training?

For most gym sessions under an hour, water is plenty. Sports drinks with electrolytes and carbohydrates become relevant for long efforts (over 60 to 90 minutes), intense work or hot weather, when you sweat a lot and lose sodium. Otherwise they mainly add unnecessary sugar: a pinch of salt and some water often cover the need.

Can you drink too much water while exercising?

Yes, it's rare but real. Drinking huge amounts of plain water during a very long effort, with no sodium intake, can dilute the blood and cause hyponatremia, which is dangerous. For the recreational athlete, the main risk remains dehydration, not excess. Drink according to thirst and losses, without forcing down litres at once, and add electrolytes on long efforts.

Do coffee and tea count towards hydration?

Yes, largely. Coffee and tea contribute to your fluid intake despite their mild diuretic effect, which stays modest at usual amounts. On the other hand, too much caffeine just before an intense session can heighten the feeling of a racing heart. Water remains the base, and sugary drinks or alcohol are not good ways to hydrate around training.

The bottom line

Hydration is nothing spectacular, but that's exactly what makes it so effective: a simple, free habit that immediately improves the quality of your sessions and your recovery. No need for complicated products for most workouts, just water, at the right time and in the right amount.

Remember the essentials: arrive already hydrated, drink in small sips as soon as the effort drags on or the heat rises, replace losses afterwards, and keep urine colour as your marker. Reserve electrolytes for long efforts and serious heat. The rest of the time, water and a bit of consistency do all the work.

Want coaching that links training, nutrition and daily habits to your real goal? I can help you build a plan calibrated to your body and your schedule. The first assessment session is free: 60 minutes to take stock and lay solid foundations.

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