How to stay hydrated in a heatwave

Hydration becomes crucial as temperatures climb into the 30s and beyond. Our bodies constantly generate heat—about 75 to 80% of the energy we use appears as heat—and without ways to dissipate it, body temperature can rise quickly; for example, lying still could raise it by about 1.3C in an hour.

Normally heat is lost through convection and radiation as skin blood vessels dilate, but when the outside air is as warm as or warmer than the skin (around 35–36C) that process falters and sweating becomes the main way to cool down, so fluids must be replaced. Even mild dehydration impairs body and brain function, producing headaches, fatigue, reduced concentration and poorer physical performance.

Thirst tends to lag, appearing after roughly 1–2% of body mass has been lost in fluid, so checking urine colour is a simple early indicator: very dark urine suggests dehydration, while pale urine generally means you are well hydrated. Rather than guzzling a large amount at once, drink moderate amounts regularly.

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