Short answer: Start every session well hydrated, drink enough during exercise to avoid losing more than 2% of your body weight, and replace both fluid and electrolytes afterwards. Because everyone sweats differently, the best plan is built around your own sweat rate, which you can work out with a set of bathroom scales. Zuum Performance Energy Powder combines 500mg of sodium and three other key electrolytes with 120mg of caffeine in every sachet.
Hydration is one of the simplest things you can get right in training, and one of the easiest to get wrong. This guide covers what happens when you dehydrate, how much to drink and when, and why electrolytes matter as much as water.
What happens when you get dehydrated
When you sweat more than you drink, your blood volume drops. Your heart has to work harder to push blood to your muscles and to your skin to keep you cool. The knock-on effects stack up quickly:
- your heart rate climbs for the same effort
- your core temperature rises
- exercise feels harder than it should
- your concentration and decision-making start to slip
The American College of Sports Medicine (ACSM) uses a simple line in the sand. In its position stand on fluid replacement, it recommends drinking enough during exercise to avoid losing more than 2% of your body weight through dehydration. For a 75kg athlete, that's just 1.5kg, which is easy to sweat out in a hot session.
Why one-size-fits-all advice doesn't work
Two people doing the same session can lose very different amounts of sweat. Sweat rates commonly range from about 0.5 to 2 litres an hour, depending on:
- You: genetics, body size, sex, fitness and how acclimatised you are to the heat.
- Your environment: temperature, humidity, wind and sun.
- Your session: intensity, duration and what you're wearing.
Sweat sodium varies just as much. The ACSM notes an average of about 35mmol of sodium per litre of sweat (roughly 800mg), with some people losing far more. That's why the ACSM recommends a personalised hydration plan rather than a fixed number for everyone.
How to work out your sweat rate
You only need a set of scales and a watch.
- Weigh yourself before training. Go to the toilet first, and weigh yourself in minimal clothing.
- Train as normal. Note how long you train for and how much you drink, in litres.
- Weigh yourself again afterwards. Towel off and use the same clothing as the first weigh-in.
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Do the maths:
- Weight lost (kg) = weight before - weight after
- Total sweat (litres) = weight lost + fluid you drank
- Sweat rate (litres per hour) = total sweat ÷ hours trained
Example: you weigh 80.0kg before a 90-minute session, drink 750ml, and weigh 78.9kg afterwards. You lost 1.1kg, so your total sweat was 1.1 + 0.75 = 1.85 litres. Your sweat rate is 1.85 ÷ 1.5 hours = about 1.2 litres an hour.
Your sweat rate will change with the weather. If you've got a big event coming up in hotter or more humid conditions, repeat the test in conditions as close as possible to race day.
Before exercise: start topped up
The goal is to start your session properly hydrated, not to cram fluid in at the last minute. The ACSM suggests:
- About 4 hours before: drink around 5-7ml of fluid per kg of body weight. For a 75kg person, that's roughly 375-525ml.
- About 2 hours before: if you haven't needed the toilet, or your urine is dark, have another 3-5ml per kg.
Including sodium in that drink helps. It encourages you to drink and helps your body hold on to the fluid rather than passing it straight through.
With Zuum: a sachet of Zuum Everyday Energy Powder in water a few hours out gives you 250mg of sodium, 200mg of potassium and 60mg of magnesium, plus 60mg of caffeine. If you'd rather save your caffeine for closer to the start, that's fine too.
During exercise: match what you lose
Use your sweat rate to set your drinking target. Aim to replace enough to stay within that 2% body weight limit, but don't force down more than you're losing. Over-drinking is also a risk, especially in long events.
For longer or hotter sessions, the ACSM notes that drinks containing electrolytes can offer benefits over water alone. That's because you're replacing what's actually leaving in your sweat.
With Zuum: one sachet of Zuum Performance Energy Powder in a 700ml bottle gives you:
| Per sachet | Zuum Performance Energy Powder |
|---|---|
| Caffeine | 120mg |
| Sodium | 500mg |
| Potassium | 250mg |
| Magnesium | 80mg |
| Calcium | 70mg |
| Taurine + glycine | 3,250mg |
| Vitamins | B5 and B12 |
Sip it before and during training for energy and electrolytes in the same bottle. If you're wondering whether the caffeine works against your hydration, it doesn't. We cover the research in caffeine and electrolytes: why they work better together.
After exercise: refill the tank
Once you know how much weight you've lost, you know roughly how much to put back. A widely used guideline is to drink about 1.5 litres of fluid for every kilogram lost. The extra 50% covers the fluid you'll pass as urine while you rehydrate.
You don't need to drink it all at once. Have a good drink straight after training, then keep sipping over the next few hours. Replacing sodium at the same time, through a salty meal, a snack or an electrolyte drink, helps your body hold on to that fluid.
A note on timing: both Zuum powders contain caffeine. If you train in the evening, keep an eye on your total caffeine for the day, and use water and food for your later rehydration.
Electrolytes: what they are and why they matter
Electrolytes are minerals that carry a small electrical charge once they're dissolved in your body's fluids. That charge is what lets them do their jobs:
- Sodium: the main electrolyte in your blood and the one you lose most in sweat. It's central to fluid balance and to driving thirst.
- Potassium: the main electrolyte inside your cells. It works with sodium to balance fluid and is involved in muscle and nerve function.
- Magnesium: involved in muscle and nerve function, and in turning food into energy.
- Calcium: needed for normal muscle contraction.
- Chloride: pairs with sodium to help regulate fluid balance.
Sodium and chloride are the electrolytes you lose in the largest amounts through sweat. Potassium, magnesium and calcium are lost in smaller amounts. If you only replace water after a big sweat, you can dilute what's left. That's one reason heavy sweaters can feel flat, headachy or crampy when they rely on water alone.
Getting electrolytes from food
A balanced diet covers most of your everyday electrolyte needs:
- Sodium: salted foods, bread, cheese, stock and broths.
- Potassium: bananas, potatoes, avocado, beans and yoghurt.
- Magnesium: nuts, seeds, wholegrains and dark chocolate.
- Calcium: milk, yoghurt, cheese and calcium-set tofu.
Food works well around training, but it's not always practical during a session or straight after it. That's where an electrolyte drink earns its place.
Choosing your Zuum
| Everyday Energy Powder | Performance Energy Powder | |
|---|---|---|
| Best for | Work, study, easy sessions, daily hydration | Training, game day, long or hot sessions |
| Caffeine | 60mg | 120mg |
| Sodium | 250mg | 500mg |
| Potassium | 200mg | 250mg |
| Magnesium | 60mg | 80mg |
| Calcium | - | 70mg |
| Extras | B5 and B12 | B5 and B12, 3,250mg taurine + glycine |
Both are made with organic salts and contain no artificial colours, flavours or sweeteners. Flavours:
- Everyday: Watermelon, Blackcurrant and Lychee.
- Performance: Lemon Lime, Raspberry and Passionfruit.
Frequently asked questions
How much water should I drink before exercise?
The ACSM suggests about 5-7ml per kg of body weight around 4 hours before exercise. Add another 3-5ml per kg about 2 hours before if your urine is still dark.
How do I know if I'm dehydrated?
Dark urine, thirst, a headache, and feeling unusually tired or dizzy are common signs. Weighing yourself before and after training is the most practical way to measure fluid loss.
How much should I drink during exercise?
Enough to avoid losing more than 2% of your body weight. Your sweat rate tells you roughly how much that is per hour.
Do I need electrolytes or is water enough?
For short, easy sessions, water is usually fine. For long, hard or hot sessions, or if you're a heavy or salty sweater, replacing electrolytes, especially sodium, makes a real difference.
How much should I drink after exercise?
About 1.5 litres for every kilogram of body weight you've lost, spread over the following few hours.
Does caffeine dehydrate you?
Not in moderate amounts. Research shows caffeinated drinks hydrate about as well as water. Read more here.
Key takeaways
- Losing more than 2% of your body weight through sweat can hurt both physical and mental performance.
- Start every session well hydrated, and keep drinking during it.
- Work out your own sweat rate. It's the best guide to how much you need.
- Replace electrolytes as well as water, especially sodium.
- After training, drink about 1.5 litres for every kilogram lost.
Source: American College of Sports Medicine (2007). Exercise and fluid replacement (position stand). Medicine & Science in Sports & Exercise 39(2):377-390. View on PubMed.
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