Ottawa Water Hardness & Quality Report (2026)

Ottawa's drinking water is treated and distributed by Ottawa Public Utilities (a service of the City of Ottawa), drawing from the Ottawa River via the Lemieux Island water treatment plant and from the Rideau River via the Britannia facility. These plants use coagulation, sedimentation, filtration, and chlorination, producing water fully compliant with the Guidelines for Canadian Drinking Water Quality (GCDWQ). Ottawa residents receive water measuring 88 mg/L (5.1 gpg) — classified as moderately soft to moderately hard by Health Canada.

The Ottawa River drains a vast watershed straddling the Precambrian Canadian Shield to the north and Paleozoic limestone formations to the south. Shield granite and gneiss tributaries contribute very soft water, which blends with harder limestone-influenced runoff from the Rideau Valley, resulting in the moderate hardness observed at 88 mg/L. Seasonal variation in river chemistry can cause slight fluctuations in hardness throughout the year.

At this moderate hardness level, Ottawa homeowners see light scale deposits on kettles and around tap aerators — less frequent descaling than in Alberta or Saskatchewan. Hot water tanks typically perform well without additional treatment, though scale can accumulate in older electric tanks over many years. A basic cartridge filter or magnetic scale conditioner provides adequate protection for most households.