Sainte-Thérèse Water Hardness & Quality Report (2026)

Sainte-Thérèse's drinking water is managed by Ville de Sainte-Thérèse, a historic suburb in the Thérèse-De Blainville MRC of the Laurentides region, adjacent to Boisbriand and Blainville on Highway 15 north of Montréal, drawing from the Rivière des Mille Îles — the north arm of the two channels separating Île Jésus (Laval) from the mainland. Water undergoes coagulation, sedimentation, filtration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) requirements. Hardness measures 66.5 mg/L (3.9 gpg) — classified as moderately hard by Health Canada, notably softer than the adjacent Boisbriand (112.5 mg/L) despite sharing the same administrative region.

The marked difference between Sainte-Thérèse (66.5 mg/L) and nearby Boisbriand (112.5 mg/L) reflects distinct source water character: the Rivière des Mille Îles draws primarily from the lower Laurentides drainage of the Precambrian Canadian Shield, with relatively brief contact with the Ordovician Lowlands carbonate platform, producing softer water. Boisbriand by contrast may blend a higher proportion of local Lowlands groundwater from the carbonate-rich Vaudreuil-Soulanges plain. The 66.5 mg/L supply is closer to the softer Laval and north Montreal boroughs than the harder south shore and Island communities.

At 66.5 mg/L, Sainte-Thérèse residents experience minimal scale deposits — occasional kettle cleaning every two to three months is adequate. Hot water tanks have a very good operational lifespan. Ville de Sainte-Thérèse publishes annual water quality reports following Ministère de l'Environnement standards. Health Canada lead precautionary guidance applies to residents in the community's pre-1975 single-family homes and apartment buildings near the historic town centre.