Dollard-Des Ormeaux Water Hardness & Quality Report (2026)

Dollard-Des Ormeaux (a residential suburb on the western portion of the Island of Montréal, in the West Island sector) receives its drinking water through the Régie intermunicipale de l'eau Ouest-de-l'île or municipal supply coordination, drawing from the St. Lawrence River or the Rivière des Prairies via the West Island treatment infrastructure. Treatment includes coagulation, sedimentation, filtration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) requirements. Hardness in the Dollard-Des Ormeaux distribution zone is 107.5 mg/L (6.3 gpg) — classified as moderately hard by Health Canada, one of the harder West Island supply zones, reflecting a proportionally higher direct St. Lawrence main channel supply fraction.

Dollard-Des Ormeaux's elevated hardness relative to the Montréal citywide average (~75 mg/L) reflects the West Island supply corridor's draw from a section of the St. Lawrence River where the harder Ordovician limestone Lowlands basin chemistry dominates. Compared to central Montréal boroughs that blend softer Rivière des Prairies supply with St. Lawrence mainstream water, the West Island utilities draw predominantly from the direct St. Lawrence channel, which carries a higher dissolved calcium load from the Ordovician Trenton Group carbonate strata underlying the St. Lawrence Lowlands.

At 107.5 mg/L, Dollard-Des Ormeaux residents experience moderate scale deposits in kettles and on tap aerators — descaling every six to eight weeks is typically adequate. Hot water tanks benefit from periodic inspection. As a dense West Island suburb with significant 1960s–1980s residential housing stock, residents are encouraged to follow Health Canada and Ministère de l'Environnement guidance on lead service lines and to verify lead status in older properties built before 1990.