City officials say the main break happened around 2 p.m. on St-Charles in front of the Cité-des-Jeunes secondary school. The cause is unknown.
Officials say the water service, which was cut off in the Vaudreuil sector, should be restored by the end of the afternoon.
However, there will be a boil water advisory in place for an indefinite period after the water is back on.
The Dorion sector is unaffected.