Heatwave Hydration: Do You Actually Need Electrolytes, or Just Water?

Every time the mercury climbs, the same thing happens: your feed fills up with electrolyte sachets, "hydration multipliers" and influencers swirling neon-coloured powders into water bottles. It's practically a British summer tradition at this point, right up there with hosepipe bans and complaining that it's "too hot to sleep."

But is any of it necessary, or is this just very effective marketing wearing a lab coat? We went looking for what the actual evidence and the UK's own medicines regulator say, rather than what the internet says. The honest answer is: it's genuinely a bit of both, and the people who stand to gain most from electrolyte drinks aren't necessarily who the ads are aimed at.

What Actually Happens to Your Body in Heat?

When you're hot, you sweat, and sweat isn't just water. It carries electrolytes, minerals like sodium, potassium, calcium and magnesium that are involved in things like fluid balance and muscle and nerve function. Lose enough fluid and you can end up dehydrated, which the NHS describes as feeling thirsty, having darker urine, or a dry mouth and lips [NHS, Dehydration]. The same NHS guidance is refreshingly unglamorous about prevention: drink fluids regularly, and water or diluted sugar-free squash are good choices, with more needed in hot weather or after exercise [NHS, Water, drinks and your health].

Notice what's missing from that official advice: any mention of electrolyte drinks at all. That's not an oversight, it's a fairly telling clue about where this debate actually sits.

What the MHRA Actually Advises

Here's the twist that most of the summer hydration content skips entirely. When the MHRA (the UK's Medicines and Healthcare products Regulatory Agency) put out heatwave guidance this summer, it wasn't about what to drink. It was about where you keep your medicines.

The advisory, titled "Hot cars, hot luggage: why where you store your medicines matters this summer," warns that many medicines are meant to be stored below 25°C, and that "parked cars, packed suitcases, caravans, and sunny rooms can get far hotter than people expect," according to the MHRA's Chief Safety Officer, Dr Alison Cave. Insulin, certain inhalers, some creams and some contraceptives are flagged as particularly heat-sensitive [MHRA].

The regulator has also flagged heat-related interaction risks around this year's heatwave, separately reminding people that summer habits like drinking alcohol alongside antibiotics, mixing grapefruit juice or herbal supplements such as St John's Wort with certain medications, or shifting the timing of doses while travelling, can all change how a medicine behaves [GB News, "UK heatwave: MHRA issues warning over drug interactions to watch out for this summer"]. Sensible, practical, and about medicine safety, not about which powder you stir into your water bottle.

The Electrolytes-vs-Water Debate

So where do electrolyte drinks actually fit? This is genuinely a live debate, not a settled one, and it's worth saying that plainly rather than picking a side for the sake of a tidy headline.

BBC Bitesize's look at why electrolyte drinks go viral every summer put it plainly: "most people don't actually need electrolyte supplements as our kidneys work to keep our electrolyte levels stable and we can usually top up these minerals through the foods we eat" ["Why do electrolyte drinks go viral every summer?"]

That's not the same as saying electrolyte drinks are pointless for everyone, though, and the same BBC piece is careful to say so.

Who Genuinely Benefits From Electrolytes

The BBC piece flags a couple of situations worth knowing about. One is what's sometimes called being a "salty sweater": if you get visible white salt marks on dark clothing after exercise, you're likely losing more sodium through sweat than average. The other is illness rather than heat exposure: if you've had vomiting or diarrhoea and lost significant fluid, the NHS notes that a pharmacist can recommend oral rehydration solutions, powders mixed with water designed for exactly that situation.

In other words, the people electrolyte products are genuinely built for are heavy sweaters doing prolonged, intense exercise, and people rehydrating after illness under a pharmacist's guidance, not necessarily everyone sitting in a beer garden during a heatwave.

One More Thing

We've been paying close attention to this exact debate while we work on something of our own in this space. Nothing's finalised yet, so we're not going to describe it here, but if hydration and what actually goes into it (and what doesn't need to) is something you think about in summer, keep an eye out. We'll share more when there's something worth sharing.