Heatwaves: why drinking more water isn't enough

August 8, 2026 by AUA Hydrate

When the temperature climbs, the reflex is simple: drink more. That's necessary, but not sufficient. Because in high heat it isn't only the volume of water lost that rises — it's the quantity of minerals that goes with it.

What heat really changes

Sweating is the body's cooling system. The hotter it gets, the harder it runs — and it doesn't only put out water. Sweat is salty, and that sodium loss is far from trivial: over a summer's day spent outdoors, it is counted in grams.

Add potassium and magnesium to that, and you have a deficit no glass of water, however large, will fill.

The plain-water trap

Drinking a lot of water without minerals, when you have already sweated heavily, amounts to diluting still further a body that is short of salt. The body reacts by flushing out the excess to restore the balance — hence that frustrating sensation of drinking constantly, going to the toilet often, and still feeling tired.

That is exactly the mechanism described in Why water alone is no longer enough, but amplified by the heat.

Summer's warning signs

• The mid-afternoon headache, even though you have been drinking.
• Night cramps after a hot day, even without exercise — a subject covered in Cramps and headaches.
• Unusual tiredness at the end of the day, without any particular effort.
• Dark urine despite a normal water intake.

Adapting your hydration in the heat

• Get ahead of it. Start the day hydrated rather than catching up in the evening. One stick of AUA Hydrate in 500 ml on waking sets the base.
• Drink regularly, not massively. Sips every 20–30 minutes beat a litre in one go.
• Salt your meals normally. In high heat this is not the moment to cut salt — unless your doctor says otherwise.
• Beware false solutions. Alcohol and very sugary soft drinks make dehydration worse rather than correcting it.

Who should pay most attention

1. Older people, whose sense of thirst dulls with age.
2. Anyone working or training outdoors: losses can exceed 2 litres an hour.
3. Children, who cool themselves less efficiently than adults and rarely think to drink on their own.