How Much Sodium Do You Actually Need in an Electrolyte Drink?

Walk down any hydration aisle and every product promises to "replenish electrolytes." But the number that actually decides whether a drink hydrates you properly is one most brands keep quiet about: sodium. Get it right and you genuinely rehydrate. Get it wrong — which most drinks do — and you're mostly drinking flavoured water.

Here's what the science says about how much sodium you actually need, and how to spot a drink that's underdosed.

Why sodium is the electrolyte that matters most

You lose several electrolytes when you sweat — potassium, magnesium and calcium among them — but sodium is lost in by far the largest amount, and it's the one that drives how well your body absorbs and holds onto fluid. Potassium losses in sweat are relatively small (often around 150–250mg per litre), while sodium losses dwarf them.

That's why sodium is the headline number to check. Without enough of it, water passes straight through you rather than actually rehydrating you — and in prolonged heavy sweating, drinking lots of plain water without replacing sodium can even dilute your blood sodium too far, which is a genuine health risk, not just a performance one.

How much sodium do you actually lose?

This is where the numbers get useful. Research on athletes and heat-exposed workers consistently puts average sweat sodium loss at roughly 800 to 950mg per litre of sweat. But the individual range is enormous: some people lose as little as 200mg per litre, while "salty sweaters" — you'll recognise them by the white, gritty streaks left on skin and clothing — can lose up to 2000mg per litre.

And you can sweat a lot. Sweat rates commonly sit around a litre an hour during exercise and climb higher in heat. So an hour of hard training in warm conditions can easily cost you 800–1000mg of sodium or more — from a single session.

The problem with most "hydration" drinks

Here's the uncomfortable maths. A typical sports drink contains only around 100mg of sodium per serving. If you've lost 800–1000mg through sweat, that barely touches the sides — you'd need to drink many bottles to replace what one session took out, and you'd swallow a large amount of sugar doing it.

This is the gap most brands don't want you to notice. A drink can be marketed on hydration, taste great, and still deliver a fraction of the sodium your body actually lost. Flavour is easy. Adequate sodium is the part that counts, and it's the part that's usually missing.

So what's the right amount to look for?

For general daily hydration and lighter activity, you don't need aggressive sodium levels — but you do want a meaningful dose, not a token 100mg. For anyone training, sweating heavily, working in heat, or on the higher end of the sweat spectrum, a drink providing closer to 1000mg of sodium per serving is far better matched to what you actually lose in an hour of sweat.

A sensible checklist when you read a label:

• Sodium: look for a real dose. Around 1000mg per serving properly matches an hour of typical sweat loss; 100mg does not.
• Supporting electrolytes: potassium and magnesium should be present too, as you lose those as well — just in smaller amounts.
• Sugar: you don't need sugar to hydrate. High sugar is a sign the drink is built around taste, not mineral replacement.

Where Siply sits

This is exactly why we built Siply the way we did. Each sachet delivers 1000mg of sodium, alongside potassium and magnesium, with zero sugar and just 10 calories. It's designed to match what your body genuinely loses through sweat — not to be the sweetest thing on the shelf.

If you sweat heavily, train regularly, or you're simply tired of "hydration" drinks that are mostly sugar and flavour, a proper sodium dose is the difference between drinking something and actually rehydrating. You can explore the full Siply electrolyte range here — zero sugar, 1000mg sodium, and £1 from every order goes to mental health charity If U Care Share.

A quick note: sodium needs are individual, and if you have high blood pressure, kidney concerns or any condition affecting your sodium intake, check with your GP before significantly increasing electrolyte use.