Nodava urges all with municipal water in Grövelsjön to boil drinking water until further notice as a precaution.
Norra Dalarnas vatten och avfall, Nodava, issued the recommendation on its website on Friday afternoon. The company reacted to a test result from routine sampling.
Customers are urged to boil water used for cooking, drinks, pet drinks and tooth brushing. The cause is being investigated and new samples will be taken.
Updates on the disturbance are published continuously on Nodava's website.