If you have ever finished a run in Johannesburg heat, drunk a litre of water, and still felt flat an hour later, you have already met the problem this article solves. Water alone does not fix dehydration. What you lose in sweat is water and salt, and replacing only half of that pair can leave you feeling worse rather than better.
This guide explains what electrolytes actually are, how much you lose, how to tell when you are short, and how to replace them without loading up on sugar. It is written for people who train, work outdoors, or simply live somewhere hot — not for a laboratory.
What electrolytes actually are
Electrolytes are minerals that carry an electrical charge when dissolved in water. That charge is not a metaphor. Your nervous system runs on it: every nerve impulse and every muscle contraction depends on charged particles moving across cell membranes in a controlled sequence.
The ones that matter most for hydration are:
- Sodium — the main electrolyte lost in sweat, and the one that governs how much fluid your body holds on to.
- Potassium — works opposite sodium across the cell membrane; central to muscle contraction and heart rhythm.
- Magnesium — involved in more than 300 enzyme systems, including muscle relaxation and energy production.
- Chloride — travels with sodium and helps maintain fluid balance and blood pH.
- Calcium — required for the muscle fibre to contract at all.
Note the pairing: sodium and potassium are antagonists, and magnesium and calcium are antagonists. Hydration is not about maximising any single mineral. It is about keeping ratios in a workable range.
How much you actually lose in sweat
This is where most advice becomes vague, so here are real numbers. Sweat rates during exercise typically fall between 0.5 and 2.0 litres per hour, and can go higher in heat for a large, fit, heat-acclimatised person. Sweat sodium concentration varies enormously between individuals — roughly 200 to 2,000 mg of sodium per litre, with most people somewhere in the middle.
Multiply those out and the spread is stark. A light sweater losing 0.5 L/hour at 400 mg/L loses 200 mg of sodium in an hour. A heavy, salty sweater losing 1.8 L/hour at 1,500 mg/L loses about 2,700 mg in the same hour — more than a full day's worth of moderate sodium intake, gone in sixty minutes.
That range is the single most important thing to understand about hydration advice: there is no universal number. If you finish a session with white salt rings on a dark shirt or gritty salt on your face, you are at the high end and generic guidance will under-serve you.
A simple way to measure your own sweat rate
- Weigh yourself, undressed, immediately before a one-hour session.
- Train for exactly an hour. Note how much fluid you drink, in millilitres.
- Towel off and weigh yourself again.
- Sweat loss (litres) = weight lost (kg) + fluid drunk (litres).
A kilogram of body mass lost is roughly a litre of sweat. Do this in a few different conditions — cool morning, hot afternoon — and you will learn more about your own hydration needs than any generic chart can tell you.
Signs you are short on electrolytes
Dehydration and electrolyte depletion overlap but are not identical. The symptoms below are the ones people most often report:
- Muscle cramps or twitching, especially in the calves and feet
- Fatigue that is out of proportion to the effort
- Headache, particularly a dull ache in the afternoon
- Difficulty concentrating, or a foggy, slow feeling
- Light-headedness when standing up quickly
- Nausea, especially if you have been drinking plain water heavily
That last one deserves emphasis. Drinking large volumes of plain water while losing a lot of sodium dilutes the sodium remaining in your blood. In its serious form this is called exercise-associated hyponatraemia, and it is genuinely dangerous — it has caused deaths in endurance events. The symptoms early on look confusingly like dehydration: headache, nausea, confusion. The instinctive response, drinking more water, makes it worse.
This is the practical argument for salt in your drink rather than more water in your bottle. If you are sweating heavily for more than about an hour, plain water is not the safe default that people assume it is.
Why water alone is not enough
Sodium does two useful things in a rehydration drink, and neither is about flavour.
First, it drives absorption. Glucose and sodium are co-transported across the wall of the small intestine, and water follows them by osmosis. This is the mechanism behind oral rehydration therapy — the World Health Organization's oral rehydration salts formula is built on exactly this principle, and it is credited with saving millions of lives from dehydrating illness. A little sodium and a little carbohydrate together move water into you faster than water on its own.
Second, sodium determines retention. Drink plain water and blood sodium falls slightly; your body reads that as "too much fluid" and sends it to the kidneys. You urinate out a meaningful fraction of what you just drank. With sodium present, more of it stays where you need it.
The practical version: after a hard, hot session, a litre of plain water is partly wasted. A litre with sodium in it is not.
Magnesium, zinc and B6: the supporting cast
Sodium and potassium do the acute hydration work. The other ingredients in a well-built formula are there for recovery rather than for fluid balance.
Magnesium is a cofactor in over 300 enzyme systems, including those that regulate muscle contraction and the production of ATP, your cells' energy currency. Where sodium and potassium make a muscle contract, magnesium is involved in letting it relax again. Dietary surveys in many countries consistently find a substantial share of adults falling below recommended magnesium intakes.
Zinc supports normal immune function and protein synthesis. It is also lost in sweat, which is why people training heavily in hot conditions are a group of interest for zinc status.
Vitamin B6 is required for the metabolism of amino acids and for the release of glucose from stored glycogen. Its role here is metabolic support, not hydration.
L-glutamine is the most abundant free amino acid in the body and a fuel source for the cells lining the intestine.
A word on honesty: none of these are magic, and none of them will rescue a bad training block or a bad night's sleep. They are there so that a drink you are taking anyway for hydration does a bit more work while it is in you. Our full ingredient list, with the reasoning for each, is on the product pages.
The sugar problem
Traditional sports drinks were designed for a specific job: fuelling continuous endurance efforts lasting more than about ninety minutes, where topping up blood glucose genuinely improves performance. For a Tour de France stage, the sugar is the point.
The problem is that the same formula gets marketed for a 40-minute gym session, a hot commute, or a hangover, where the carbohydrate load is simply surplus energy. A typical 500 ml sports drink carries around 30 g of sugar — comparable to many soft drinks.
If your goal is hydration rather than fuelling, you want the electrolytes without the sugar load. That is the entire design brief behind a zero-cane-sugar formula: keep the sodium, keep the magnesium, drop the calories you did not need. We have written about this trade-off in more depth in our piece on clean hydration.
How to actually use electrolytes
Timing matters less than most marketing suggests, but a few principles hold up:
- On waking. You have gone seven or eight hours without fluid while still losing water through breathing. A morning electrolyte drink is the easiest habit to build. See the morning hydration routine for the detail.
- Before heat or hard effort. Drinking 400–600 ml with electrolytes in the two hours before a hot session starts you topped up rather than playing catch-up.
- During anything over an hour in the heat. This is where sodium stops being optional.
- After. Replace roughly 1.25 to 1.5 litres for every kilogram of body mass lost, with sodium present so that you retain it.
- When ill. Vomiting and diarrhoea lose fluid and electrolytes fast. This is oral rehydration's original use case.
Who should be careful
Added sodium is not right for everyone. Speak to a doctor before adding an electrolyte supplement to your routine if you have high blood pressure, kidney disease, or heart failure, or if you take diuretics, ACE inhibitors, or potassium-sparing medication. Sodium and potassium loads interact with all of these. The same applies during pregnancy.
This is not legal boilerplate — sodium and potassium balance is genuinely clinically significant, and a product designed for a heavy sweater in summer is not automatically appropriate for someone managing hypertension.
The short version
Sweat costs you water and salt. Replacing only the water leaves you flat, and in extreme cases makes you unwell. Work out roughly how much you sweat, get some sodium in alongside your fluid when sessions run long or hot, and treat magnesium, zinc and B6 as useful support rather than the main event. Skip the sugar unless you are actually fuelling a long endurance effort.
If you want to try that approach, our full range is built on it, and the FAQ page covers the practical questions about mixing and dosing.
