Saint-Laurent Water Hardness & Quality Report (2026)

Saint-Laurent (a west-island borough of Ville de Montréal) receives its drinking water through Ville de Montréal — Direction de l'eau potable, supplied from the integrated municipal network drawing from the St. Lawrence River and Rivière des Prairies via the Atwater, DesBaillets, and Charles-J. Des Baillets water treatment plants. Treatment includes ozonation, biofiltration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) standards. Hardness in Saint-Laurent's distribution zone is 81.5 mg/L (4.8 gpg) — classified as moderately hard by Health Canada, slightly harder than the eastern Montréal boroughs, reflecting a higher proportion of St. Lawrence mainstream supply relative to Shield-influenced Rivière des Prairies tributary inflow in this west-island zone.

Saint-Laurent's supply is drawn from a distribution zone closer to the primary Atwater and DesBaillets St. Lawrence treatment points, where the balance of harder Ordovician limestone-influenced mainstream St. Lawrence water and softer Shield tributary inflows produces 81.5 mg/L — somewhat higher than the 69–73 mg/L measured in the Rivière des Prairies-dominant boroughs of northern and east-central Montréal. This modest hardness difference reflects the west-island zone's direct connection to the St. Lawrence intake corridor.

At 81.5 mg/L, Saint-Laurent residents experience moderate scale deposits in kettles and on tap aerators — descaling every two to three months is generally adequate. Hot water tanks perform reliably at this hardness without dedicated scale treatment. Saint-Laurent's dense commercial and residential development includes a mix of post-war and modern housing; Montréal's Direction de l'eau potable advises residents in older properties to check for lead service lines and to access the city's free lead testing and replacement programme in compliance with Health Canada guidelines.