Chemicals approved to prevent brown tap water on Læsø

Læsø Municipality has received permission to add chemicals to its drinking water supply in an effort to eliminate persistent discoloration, DR reports. The measure follows years of complaints from residents and tourists about brown water flowing from taps, particularly during peak seasons.

The utility provider, Læsø Forsyning, will introduce two chemicals—Magnafloc, a flocculant, and polyaluminium chloride, a coagulant—to bind organic particles in the water, making them easier to filter out at treatment plants.

“We don’t want the water to be brown,” said Hanne Krogh, director of Læsø Forsyning. “Our goal is to deliver clean water to everyone.”

Experts confirm the treated water will remain safe. Hans-Jørgen Albrechtsen, a professor at DTU’s Department of Water and Environmental Engineering, noted that while aluminium and chloride levels will rise, they will stay below regulatory limits. “The water must be considered healthy and clean,” he stated.

Cause of discoloration

The brown tint stems from disturbed sediment in pipes—including ochre and organic matter like humus—when water flow increases, especially during tourist-heavy periods. Flushing fire hydrants and pipes has been the primary mitigation method until now.

While chemical treatment for discoloration is rare in Denmark, Albrechtsen said it is standard practice in many European countries to clarify surface water. Frederikshavn Municipality approved the measure.

Residents like Pernille Jonasson, who has dealt with brown water for years, welcomed the change. “I’m not usually sensitive about it, but during Easter, sand even settled in the shower after bathing,” she said. “I don’t want my children bathing in that.”