Annex Water Hardness & Quality Report (2026)

The Annex (one of Toronto's most beloved and historic neighbourhoods, stretching from Bloor Street West to Dupont, between Spadina Avenue and Avenue Road, home to the University of Toronto and a dense mix of Victorian houses and apartment buildings) receives its drinking water from the City of Toronto, drawing from Lake Ontario via the R.C. Harris Water Treatment Plant on the eastern lakeshore. Water is treated using ozonation, biofiltration, UV disinfection, and chloramination, meeting all Guidelines for Canadian Drinking Water Quality (GCDWQ) standards. Hardness in this distribution zone is 239 mg/L (14.0 gpg) — classified as very hard by Health Canada, with TDS of 605 mg/L, consistent with central Toronto's characteristically very hard supply.

The Annex receives R.C. Harris plant Lake Ontario supply through the central Toronto distribution network — the same fundamentally very hard Lake Ontario water (dissolved Silurian and Devonian carbonate from the Great Lakes basin, 235–240 mg/L) that serves all Toronto boroughs. The 239 mg/L is characteristic of the Annex–Midtown corridor, consistent with Church-Yonge Corridor (240 mg/L) and Dovercourt-Wallace Emerson-Junction (237.5 mg/L) sub-zones in the same supply zone.

At 239 mg/L, Annex residents — in a neighbourhood dense with pre-1930 Victorian and Edwardian houses converted to apartments and student rentals — face persistent scale challenges. Kettle and showerhead descaling every one to two weeks is standard. The Annex's large rental housing stock and proximity to the University of Toronto makes lead service line awareness particularly important; the City of Toronto's lead service line programme, available at toronto.ca/water, is a key resource for residents and landlords in this heritage-dense neighbourhood with significant pre-1950 plumbing.