Residents who get their water from the Shawnigan Lake North water system are complaining of a metallic odour and taste.
The Cowichan Valley Regional District believes it may be caused by algae.
A water sample has been sent to a lab for testing and people should know in about a week what the source of the metallic taste it.
The CVRD says this has happened in the past and it has been determined to be a brown algae that is not a health risk to people.
The regional district says people do not need to worry that it might be blue-green algae, which is toxic.
The CVRD says Shawnigan Lake does not have the kind of water conditions required for that strain of algae to thrive.