A boil water advisory is now in effect in Brossard, Lemoyne, St. Lambert and Greenfield Park.
The order was put in place Thursday afternoon, because of fecal coliform bacteria found in a water sample.
Residents are being advised to boil their water for at least one minute before drinking it.
A similar order for residents of Chateauguay has been in effect since Wednesday, and will remain in effect until at least Friday, when new test results will become available.