How to Hydrate in a Heatwave: Why Drinking More Water Isn't the Answer

A client, she was [52], deep in perimenopause, rang me during the last heatwave genuinely frightened. She had done everything she'd been told. Four litres of water. More than she'd ever drunk in her life. And she felt worse than when she started: pounding headache, queasy, wrung out, and oddly puffy. “I'm drinking so much water,” she said. “Why do I feel awful?”

Because water, on its own, is not hydration.

If you've ever wondered how to hydrate in a heatwave, the answer goes far beyond simply drinking more water.

What hydration actually is

Let's be clear: hydration is not the volume of water you pour in. It is water held in the right place and in the right concentration, and what decides that is your electrolytes. Sodium, potassium, chloride, and magnesium. Minerals that carry a charge and that your cells use to decide where water goes and whether it stays.

Now, here's what you lose when you sweat. Not just water. Sweat is salty; you can taste it, and along with the water go sodium, chloride, potassium and magnesium.

So if you replace only the water and none of the minerals, you have not restored the balance. You have diluted it. Do you see what I mean? You can be pouring water in and getting further from being hydrated with every glass.

The mistake almost everyone makes

We've all absorbed the same rule: drink until your pee runs clear. And it is wrong.

The UK Health Security Agency has been quite specific about this. Pale, straw-coloured urine is the sign of healthy hydration. Clear urine can mean overhydration, which disrupts your electrolyte balance and can make you feel worse, not better.

Taken far enough, over-drinking causes hyponatraemia: sodium in the blood falls too low, diluted by the sheer volume of water. If you're learning how to hydrate in a heatwave, this is one of the most important risks to understand. Symptoms start unremarkable: nausea, headache, fatigue, and a bloated, puffy feeling, which is exactly why it gets missed and why people respond by drinking even more. At the severe end, it becomes a genuine emergency. There are documented cases from the London Marathon of runners hospitalised not from dehydration but from drinking too much water.

So the target is not a number of litres. The target is pale straw. Really.

How to hydrate properly in the heat

1. Drink to the colour, not to the litre count

Pale straw, and you're passing urine reasonably regularly through the day. If it's dark and there's little of it, drink. If it's water-clear and you feel oddly rough, ease off and get some minerals in.

2. Put the salt back if you're actually sweating

Not for pottering about a cool office, but if you're gardening at 30°C, training, commuting on the Tube, or sweating through the night, you are losing sodium, and it needs replacing. A pinch of good salt in a glass of water, a proper electrolyte sachet, or simply salting your food generously on hot days. This is one of the few times I will genuinely say'eat more salt'.

3. Eat your water; this is the naturopathic bit

Here's what I love about this: food hydrates you better than water does, because it arrives with the minerals already attached. Cucumber, watermelon, tomatoes, celery, courgette, berries, oranges, leafy greens, and avocado are all mostly water, all delivering potassium alongside it. Coconut water. A cold soup. Even a bowl of yoghurt.

Potassium is the partner sodium needs, and most of us run low on it while running high on the wrong kind of salt. Can you imagine solving a heatwave with a plate of tomatoes and a pinch of salt rather than a fourth litre of water? Absolutely.

4. Sip, don't flood

Your kidneys can only process so much at once. Spread it across the day. A litre in ten minutes mostly ends up in the loo, taking your minerals with it.

5. Magnesium, quietly

Lost in sweat, involved in over 300 enzyme reactions, and a common gap. Leafy greens, pumpkin seeds, beans, or magnesium glycinate if you already know you're short.

6. Be honest about caffeine and alcohol

Tea and coffee do count toward your fluids; that myth needs to die. But alcohol is genuinely dehydrating and fragments the back half of your sleep, which in a heatwave you cannot afford. In hot weather, sleep is already under attack.

Why perimenopause makes heat harder, and it isn't in your head

This is the part almost nobody says out loud, so let me.

Your thermostat lives in the hypothalamus. When oestrogen falls, certain neurones there, the KNDy neurones, become hyperactive and start sending false signals to your temperature-control centre. It responds by dilating the blood vessels in your skin: heat, sweating, and a racing heart. That's a hot flush.

Now add 32°C outside. You are running a thermostat that has already lost some of its calibration in an environment that is stress-testing it. Of course you feel worse than everyone around you. You are not being dramatic, and you are not failing at summer. Your physiology is doing two hard jobs at once.

Practically: more sweating means more mineral loss, so the salt and potassium points above matter more for you, not less. And the usual hot-flush aggravators, sugar, alcohol, poor sleep, and stress all stack on top of the heat.

Who needs to be more careful

● Older adults: thirst signalling genuinely declines with age, so “drink when thirsty” stops being a reliable instruction. Drink to a schedule, and check on people who live alone.

●        Anyone on diuretics, blood pressure medication, SSRIs or lithium; several of these affect fluid and sodium balance. Ask your pharmacist how heat interacts with your specific prescriptions, and never stop or adjust medication yourself.

● Pregnancy, heart, lung, kidney or diabetes-related conditions all raise the risk in extreme heat.

●        Anyone with a history of low sodium, talk to your GP before adding or restricting salt.

Know the difference, because one is an emergency. HEAT EXHAUSTION: tiredness, weakness or faintness, headache, muscle cramps, feeling sick, heavy sweating, intense thirst. Move somewhere cool, drink, and cool the skin; improvement should come within 30 minutes. HEATSTROKE: confusion, lack of coordination, fast heartbeat, fast breathing or breathlessness, hot skin that is NOT sweating, and seizures. Heatstroke is a medical emergency; call 999 and cool the person while you wait. Do not wait to see if it passes.

Key takeaways

●        Hydration is water plus electrolytes; water alone can dilute you

●        Aim for pale straw urine, not clear, and not a fixed litre target

●        If you're sweating properly, replace sodium , and get potassium from food

●        Water-rich food hydrates better than water, because the minerals come with it

●        Perimenopause genuinely makes heat harder; that's thermoregulation, not weakness

●        Heatstroke is a 999 call, not a lie-down

FAQs

How much water should I drink in a heatwave?

There isn't a universal number, and chasing one is how people get into trouble. Drink to a pale straw colour, more if you're sweating, and put minerals back alongside it.

Do I need expensive electrolyte sachets?

Usually not. A pinch of salt, potassium-rich food and normal meals cover most people. Sachets earn their place with heavy sweating, endurance exercise, or illness with vomiting or diarrhoea.

Does coffee dehydrate me?

Not meaningfully at normal intakes, tea and coffee count toward your fluids. Alcohol is the one to watch.

Is clear urine really a bad sign?

It can indicate over-hydration, which disrupts electrolyte balance. Pale straw is the target.

Why do I feel worse in the heat than everyone else?

If you're in perimenopause, your thermostat is genuinely recalibrating. Medication, thyroid function, low iron and blood sugar swings all play in, worth investigating rather than enduring.

Conclusion

The instruction we've all been given, drink more water, is not wrong so much as incomplete. And in a heatwave, incomplete advice is how people end up feeling worse while doing everything right

Water, plus minerals, plus food that carries them. Pale straw, not clear. Salt when you sweat. And a body you've learned to actually read, rather than a number you're chasing.

Want to understand what your body is actually asking for? Comment 'ROADMAP' or book a free Health Roadmap consultation; let's look at the full picture.

Research & references

Heat-health alerts & hot weather guidance, UK Health Security Agency, Beat the Heat / Heat-Health Alert system. https://www.gov.uk/government/collections/heatwave-plan-for-england

Heat exhaustion & heatstroke: symptoms and when to call 999, NHS. https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/

Over-drinking & hyponatraemia: a documented case, Draper et al., overdrinking-induced hyponatraemia at the 2007 London Marathon, BMJ Case Reports, 2009. https://pmc.ncbi.nlm.nih.gov/articles/PMC3027820

Fluid intake, sweat sodium & hyponatraemia risk: modelling study, Br J Sports Med. https://pmc.ncbi.nlm.nih.gov/articles/PMC2492017

Hot flushes, KNDy neurones & thermoregulation: Menopause overview, Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/21841-menopaus

Magnesium, a cofactor for 300+ reactions, NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/