A routine sample showed that the drinking water may contain E. coli, a bacterium that can cause stomach illness.
The entire city of Östersund is affected, only two areas are excluded - Torvalla and Brunflo. No outer areas are affected either, says Roland Olsen, the municipality's media communicator.
Residents in parts of Östersund, Lugnvik, Frösön, Odensala, Fannbyn, Svedje and Orrviken are now recommended to boil all water used for drinking or cooking.
New samples have been taken and will be sent for analysis.
