Residents in Canton Bern have been told to boil their tap water after their local supply was contaminated by a major thunderstorm. Authorities say it may take days before the water supply is safe to drink.

Major thunderstorm contaminates water in Canton Bern

On Sunday and throughout most of last week, heavy thunderstorms dominated the weather in Switzerland, leading to significant damage in rural areas and towns in the mountains. Canton Bern was hit the hardest by the heavy rain, resulting in flooding in several areas.

This flood water has now made it into the canton’s supply of drinking water, with authorities now instructing residents to boil their tap water before consuming it. EWK - the main water and energy supplier in the area - warned the residents of Herzogenbuchsee, Aeschi (Steinhof), Hellsau, Höchstetten, Seeberg, Thörigen and Willadingen to start boiling their contaminated water supply on Thursday.

Drinking the water risks illness, Bernese authorities say

In a statement, the company said, “Boiling guarantees the killing of pathogens. We recommend using mineral water for drinking and in baby food. If you have already consumed the polluted drinking water, observe yourself - if you develop a high fever, diarrhoea and / or vomiting within 48 hours, consult a doctor.”

Washing dishes and brushing your teeth with the water also carries a risk of contamination, but showering, washing clothes and using the dishwasher should be okay, according to the EWK. "The drinking water is now being treated and a mains flushing is being carried out. As a result, the water may have a distinct odour or taste of chlorine over the next few days,” the company explained.

The EWK added that it will take several days before the supply is restored, and will inform those affected when it is safe to drink the water once again.