London Water Hardness & Quality Report (2026)

The Corporation of the City of London provides water to roughly 420,000 residents in Middlesex County and the city itself. The primary surface water source is the Thames River, with water treated at the Greenway and W12A plants. This supply is augmented by groundwater wells that tap into local aquifers. Distribution extends throughout urban London and nearby regions, managed by a comprehensive system of treatment and pumping stations. The Thames River watershed, a vast area covering over 8,000 square kilometers, is characterized by limestone and shale bedrock dating back to the Paleozoic era, influencing the surface water quality.

The region's water originates from a mixed geology featuring Paleozoic formations, including Devonian and Silurian limestones and dolomites like the Salina and Bass Islands groups. These carbonate rock layers readily dissolve calcium and magnesium ions as water moves through them. This natural leaching process imbues the water with minerals, contributing to its character. The presence of limestone aquifers and river sediments results in a harder water profile when compared to supplies drawn from glacial or granitic terrains found in other parts of Canada.

Homeowners in London often notice the effects of this moderately hard water, with limescale buildup being a common issue in appliances like kettles, dishwashers, washing machines, and hot water heaters. This buildup can decrease efficiency and shorten the lifespan of these devices. Fixtures might develop stains, and you may find yourself using more detergent for laundry and dishes. Simple measures like regular descaling with vinegar, installing strainers, and flushing water heaters can help manage the problem. Many residents find that installing a whole-house water softener is the most effective solution to protect their plumbing and improve cleaning performance.