You're sweating through your shirt by 8am. Your legs are cramping at 3pm. By 4 o'clock you've got a headache and your brain feels like it's running on dial-up. You drink more water but nothing shifts.
That's not dehydration. That's electrolyte depletion — and water doesn't fix it.
Here's what's actually happening and how to sort it cheaply.
What Electrolytes Actually Are (And Why Tradies Lose Them Faster)
Electrolytes are electrically charged minerals that your body uses to do almost everything. The main ones are:
Sodium — controls fluid balance, nerve transmission, and muscle contraction. You lose the most of it through sweat.
Potassium — works in opposition to sodium to regulate fluid inside and outside cells. Critical for muscle function.
Magnesium — involved in over 300 enzymatic reactions. Key for muscle relaxation, sleep quality, and energy production. Depletes rapidly with physical activity and sweat.
Chloride — mostly works alongside sodium to maintain fluid balance.
When you sweat, you're not just losing water. You're losing a solution of all of the above — particularly sodium and chloride (that's why sweat tastes salty). The more you sweat, the more you lose. The more you move, the more you sweat.
The average office worker loses maybe 500ml-1L of sweat per day. A tradie working in moderate temperatures might lose 1.5-2.5L. In summer, or doing heavy physical work — roofing, concreting, demolition — that can hit 3-4L in a single day.
Your body cannot sustain that loss without replacement.
The Symptoms of Electrolyte Depletion on Site
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Most people think dehydration just means thirst. It doesn't. By the time you're thirsty, you're already behind. And by the time electrolytes are significantly depleted, you'll have symptoms that don't feel like thirst at all.
Muscle cramps. The classic sign. Usually hits the calves, hamstrings, or feet. Sodium and magnesium both regulate muscle contraction — without them, muscles go into uncontrolled spasm. If you're cramping during work or waking up in the night with cramps, electrolytes are a primary suspect.
Afternoon energy crash. Not the “I need a coffee” crash — the “my body feels like lead and I can't think straight” crash. This often hits around 2-3pm and is partially a blood sugar thing, but electrolyte depletion is a significant contributor. Your cells literally can't generate energy efficiently without adequate sodium and potassium.
Headaches. Low sodium causes the brain to swell slightly against the skull — you feel this as a dull pressure headache, often behind the eyes or across the forehead. It's not dehydration in the simple sense. Drinking more plain water can actually make it worse because it dilutes the remaining sodium further.
Brain fog. Electrolytes are essential for nerve signal transmission. Low levels mean slower signals — you notice this as difficulty concentrating, slow reactions, or that general feeling of being unable to “get going” even when you're not physically tired.
Nausea. Severe depletion causes nausea and sometimes vomiting. If you've ever felt sick despite drinking water on a hot day on site, this is probably why.
Why Water Alone Isn't Enough When You're Sweating Through Your Shirt
There's a concept called hyponatraemia — low blood sodium — that's caused by drinking too much water without replacing electrolytes. It sounds counterintuitive but it's well documented in endurance athletes and increasingly in manual workers in hot conditions.
When you sweat heavily and replace fluid with plain water, you're diluting the electrolytes that remain in your blood. Your body's response is to shed more water through urination to try to restore the concentration — which means your hydration effort is partially self-defeating.
Plain water is fine when sweat losses are modest — mild weather, moderate activity, short duration. It's not fine when you're sweating heavily for 6-10 hours in warm conditions. In those circumstances, you need to be replacing the electrolytes alongside the fluid.
This isn't a fringe health claim. It's basic physiology. And it explains why tradies can drink seemingly adequate amounts of water and still feel rough by the afternoon.
The Cheapest Electrolyte Fix: DIY vs Sports Drinks
Here's where most advice goes wrong: it points you towards branded electrolyte drinks at £2-3 a pop. Sometimes that makes sense. Often it doesn't.
The DIY fix:
500ml water
A pinch of table salt (about 0.5g — a small pinch between your fingers) — sodium and chloride
A banana — roughly 400mg potassium, some magnesium
Total cost: about 25-30p. That's it.
For most situations, this is all you need. The pinch of salt is delivering approximately 200-250mg sodium. The banana covers potassium. Together with your food (which provides most of your mineral intake on a normal day), this keeps you topped up through a working day.
Comparison with a branded sports drink:
A standard 500ml sports drink (Lucozade Sport, Powerade, etc.) contains roughly 250-450mg sodium and 100-150mg potassium. Costs £1.50-2.50. Also contains 30-35g of sugar — which spikes your blood glucose, delivers a temporary energy hit, then drops you.
The maths: the DIY version delivers comparable or better electrolyte content for 1/8th the cost and without the sugar crash.
Electrolyte powder/tablets (like High5 Zero or Nuun) are the middle ground — low sugar, more precise electrolyte content, about 40-60p per serving. Worth having if you don't want to carry bananas and salt.
When Sports Drinks Are Actually Worth It
Sports drinks aren't entirely useless. There are specific situations where the sugar content is actually helpful:
During heavy work lasting more than 90 minutes — if you're working at high intensity (demolition, heavy labour, roofing in summer heat) for extended periods, your muscles can benefit from easily accessible carbohydrates. A standard sports drink delivers both fuel and electrolytes in one.
Post-work recovery — a small sports drink after a hard physical day aids glycogen replacement alongside electrolytes. Fine as an occasional tool.
When you're already depleted and need rapid recovery — if you've got cramps or nausea from significant depletion, a sports drink is a quick fix.
When they're a scam: when you're doing moderate work, it's not that hot, and you're just thirsty. You're paying £2 for 35g of sugar and slightly salty water. Have water and a banana instead.
How to Build an On-Site Hydration Protocol
The problem with hydration advice is that it's always retroactive — drink when you're thirsty, check your urine colour, etc. By the time those signals appear, you're already behind.
Build a protocol that's proactive. Here's a practical one:
Before work (5:30-6am): 500ml water with breakfast. Aim to start the day fully hydrated — you've been sleeping without fluid for 6-8 hours. If your urine is dark yellow first thing, that's a dehydration signal from overnight.
Mid-morning (9-10am): 500ml water + pinch of salt, or an electrolyte tablet. You've been working for 3-4 hours. This is the window where most tradies start falling behind.
Lunch (12-1pm): 500ml water with your meal. Your food is delivering electrolytes too — especially if you're eating something salty or substantial. No need to overdo it.
Mid-afternoon (2-3pm): 500ml water + banana or another electrolyte hit. This is the critical window — the 2-3pm crash is largely preventable if you've been consistent. If you're struggling by 2pm regularly, this top-up is the fix.
Total fluid target on a standard day: 3-3.5L. In hot weather or heavy physical work, up to 4-5L. Spread it through the day — don't try to drink it all at once.
Hot Weather vs Cold Weather: Does It Change Anything?
Hot weather is obvious — you sweat more, you notice it, and the risk of depletion is visible. Most tradies adjust in summer.
Cold weather is the sneaky one.
In cold conditions, you still sweat during physical work — you just don't feel it as much because it evaporates quickly in cold air. Layering up also traps sweat against your body, so you're losing fluid without necessarily feeling wet.
Cold air is also dry air (especially in winter in the UK), which means you lose more fluid through breathing than you would in warm, humid air. The respiratory moisture loss is significant at high breathing rates during heavy work.
The result: tradies in winter are chronically mildly dehydrated and electrolyte-depleted in ways they don't attribute to the cold. You're not thirsty because cold suppresses thirst sensation. You're just a bit flat, a bit foggy, a bit crampy.
The protocol doesn't change much in cold weather — drink the same amounts, keep your electrolyte top-ups in. The only difference is you need to be more deliberate about it because the body's signals are quieter.
Bottom Line
Electrolytes — sodium, potassium, magnesium, chloride — are essential for muscle function, nerve transmission, and energy production. Tradies lose them faster than almost any other group.
The fix doesn't require expensive drinks. A pinch of salt and a banana in 500ml of water costs 25p and does the job. Build a four-point hydration protocol into your day (morning, mid-morning, lunch, mid-afternoon) and the afternoon crash largely disappears.
Cold weather dehydrates you silently. Don't drop the protocol when the temperature drops.