Researcher: How much water to drink in the heat

A heatwave has swept across Sweden, and increasing fluid intake is now critical to cope with the high temperatures, according to research from the Institute of Environmental Medicine at KTH.

Mare Sundström, a researcher at the institute, says there is no fixed rule for daily water intake. Office workers who move little may need only a litre a day, while those active outdoors in extreme heat could require up to ten litres.

“People often talk about a two-litre rule, but we also get fluids from food,” Sundström said.

When temperatures rise, the body redirects blood to the skin to produce sweat and cool down. Maintaining fluid levels is essential to prevent dehydration, which can cause fatigue, poor concentration, and memory issues, as well as dry mouth and lips.

Sundström advises drinking water at the first signs of these symptoms. For most healthy adults under 60, listening to thirst cues is sufficient. However, young children and older adults may not always recognise thirst and require extra attention to ensure adequate hydration.