Côte-Saint-Luc Water Hardness & Quality Report (2026)

Côte-Saint-Luc's drinking water is managed by the Ville de Côte-Saint-Luc (an independent city entirely surrounded by the Ville de Montréal on the west island), purchasing water from Ville de Montréal drawn from the St. Lawrence River via the Atwater and DesBaillets treatment plants. Treatment includes ozonation, biofiltration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) standards. Hardness measures 119.5 mg/L (7.0 gpg) — classified as moderately hard by Health Canada, at the upper boundary of the moderately hard range — consistent with the harder West Island fringe supply corridor of the Montréal metropolitan area.

Côte-Saint-Luc's 119.5 mg/L is noticeably harder than central Montréal boroughs (70–90 mg/L) and approaches the West Island harder range (Dorval 124 mg/L from batch 4, Dollard-Des Ormeaux 107 mg/L from batch 8, Côte-Saint-Luc 119.5 mg/L). The elevated hardness in Côte-Saint-Luc and adjacent communities reflects their position in the western Montréal distribution system, where supply draws proportionally more from the harder Ottawa River–influenced St. Lawrence west channel intake, where Ordovician limestone Lowlands mineral loading is higher.

At 119.5 mg/L, Côte-Saint-Luc residents experience moderate scale deposits in kettles and on tap aerators — descaling every six to eight weeks is adequate. Hot water tanks operate reliably at this hardness. Ville de Côte-Saint-Luc provides annual water quality reports following Ministère de l'Environnement standards; the city has an older and established residential population and the characteristic West Island housing stock where Health Canada lead precautionary guidance is applicable to homes built before 1975.