Canonbury Water Hardness & Quality Report (2026)

Thames Water supplies Canonbury, the fashionable inner north London district in the London Borough of Islington — a neighbourhood of Georgian and Victorian squares, the former home of George Orwell at Canonbury Square, and adjacent to the New River Walk park that follows the historic 17th-century channel that once carried water from Hertfordshire to London — from the River Lee chalk-tributary supply in the Thames Water north London distribution zone, treated at the Lee Valley Water Treatment Works complex. At 271 mg/L (19.0°Clark), Canonbury's water is very hard — consistent with the Lee Valley chalk-dominant supply that produces persistently very hard water across the Islington and north London distribution zone.

Canonbury sits in the inner north London Islington distribution zone where Thames Water delivers Lee Valley chalk supply. The Lee carries chalk groundwater from the Hertfordshire Chalk catchment through the Lee Valley reservoir chain to Islington, producing 271 mg/L with TDS 723.2 mg/L at Canonbury — very hard water consistent with the wider inner north London Lee Valley supply tier from Islington (270–280 mg/L) through Hackney and Finsbury to Stoke Newington in the same Thames Water north London distribution zone.

At 271 mg/L, limescale is a persistent and significant household problem in Canonbury. Kettles should be descaled every two to three weeks. The combi-boiler needs a fitted scale inhibitor and annual professional servicing. Washing-up liquid requires generous quantities for adequate lather. Taps and shower heads develop substantial white chalk deposits within a week to ten days; a fortnightly descaling with white vinegar or a proprietary product keeps fittings in good condition. The very hard supply at Canonbury means that the New River Walk may now carry only historical memory of Hertfordshire water — but the chalk hardness of that original Hertfordshire supply still arrives daily at every Canonbury tap.