Ile-des-Soeurs Water Hardness & Quality Report (2026)

Île-des-Soeurs (Nuns' Island — a large island borough of the Verdun district of Montréal, connected by bridge to the Verdun shore and to the Autoroute 10 Champlain bridge approaches, known for its upscale waterfront condominium towers, the Verdun Aquatic Centre, and its unique island character within the Montréal urban area) receives its drinking water from the Ville de Verdun water network, drawing supply from the St. Lawrence River via the Atwater Water Treatment Plant — Montréal's oldest and most central treatment facility on the south Saint Lawrence riverbank. Water undergoes ozonation, sedimentation, filtration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) requirements. Hardness measures 100 mg/L (5.8 gpg) — classified as moderately hard by Health Canada, consistent with the Atwater plant distribution corridor (Atwater baseline ~98.5 mg/L).

Île-des-Soeurs' 100 mg/L is consistent with the southwest Montréal Atwater supply zone — the same plant that serves Westmount's adjacent distribution (65 mg/L DesBaillets sub-zone), Mile End, and central Montréal. The 100 mg/L reflects the St. Lawrence River's dissolved calcium content at the Atwater intake, originating from the Ordovician limestone St. Lawrence Lowlands geology of the river corridor and the moderately hard Great Lakes outflow entering the St. Lawrence upstream.

At 100 mg/L, Île-des-Soeurs residents experience moderate scale deposits — descaling every six to eight weeks is adequate. Hot water tanks operate well at this hardness. Ville de Verdun publishes annual water quality reports following Ministère de l'Environnement standards. Île-des-Soeurs' predominantly modern condominium and apartment tower infrastructure features contemporary plumbing systems, but Health Canada precautionary guidance on lead applies to older pre-1978 buildings in the island's first-generation residential development near the Verdun bridge approaches.