London Water Hardness & Quality Report (2026)

London, Ontario's drinking water is managed by the City of London — Environmental and Engineering Services, using a blended supply from two sources: the Thames River, treated at the Arva and Elgin Area water treatment plants, and groundwater from wellfields tapping into the Devonian carbonate aquifer of the Elgin-Oxford region. Both sources are treated with coagulation, softening, filtration, and chloramination before distribution, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) standards. Hardness is measured at 80 mg/L (4.7 gpg) — moderately soft by Health Canada classification.

London sits within the Middlesex County portion of southwestern Ontario, where Devonian dolostone and limestone formations underlie a thick cap of Pleistocene glacial till. The Thames River drains a mixed agricultural and forested watershed, collecting moderate mineral loads from till and bedrock outcrops. The groundwater component, drawn from deeper carbonate aquifers, is somewhat harder but is blended to produce the moderate hardness observed at the tap. Seasonal variation occurs as river water flows increase in spring.

At 80 mg/L, London homes experience only light scale build-up on tap aerators and inside kettles — far less than cities relying on undiluted Great Lakes water. Hot water tanks operate efficiently without scale treatment at this hardness level. Basic descaling of kettles two to three times a year is sufficient for most households, and a whole-home water softener is generally unnecessary unless personal preference dictates.