A precautionary boil water advisory has been issued for areas west of Morden including Thornhill.

Officials say the advisory comes after an unexpected power outage on the Dunstone Water System caused a depressurization of the system.

Until further notice, residents should use boiled or bottled water for drinking, making ice, preparing beverages including infant formula, preparing food and brushing teeth.

Officials say water samples have been sent to the lab and results are expected by Sunday, Septmeber 20.

The affected area