Water hardness in London
London, Ontario tap water is moderately hard, drawn from multiple sources including lake huron primary water supply system and municipal well systems. Here is what it means at home, and the source.
What this means at home
Some kettle and showerhead scale over time, but most homes get by without a softener.
The 2024 summary report for the City of London Distribution System lists a hardness range of 96-115 mg/L as CaCO3 across sampling locations. The recorded value is the midpoint of this official range.
You likely do not need a softener. A quick test kit confirms it for your own tap.
New to this? Read hard water, explained, including whether it is safe to drink and how to test your tap.
The number, in real terms
At 96-115 mg/L as CaCO3 mg/L (5.6 to 6.7 grains per gallon), a four-person London household puts only about 1,842 grains of hardness a day through its plumbing (industry sizing convention: about 300 US gallons a day). That is a light enough load that most homes skip the softener and just descale the kettle now and then.
Scale ceiling: every 1,000 litres heated can leave at most 105 grams of scale, because that is the total mineral carried at 96-115 mg/L as CaCO3 mg/L. Real kettles and water heaters precipitate a fraction of that, but the ceiling scales with the number: London's moderately hard water leaves little behind.
How this is calculated: grains per gallon = mg/L divided by 17.1; daily grain load = gpg x 300 US gallons (the softener trade sizes in US gallons, four-person household); regeneration interval = 32,000 grains divided by the daily load; scale ceiling = mg/L carried per 1,000 L. The input figure is City of London - 2024 Water Summary Annual Report's own published number, checked 2026-07-03. Full method on the methodology page.
London water hardness questions
How hard is the water in London?
London's tap water is moderately hard, about 96-115 mg/L as CaCO3 mg/L as calcium carbonate (5.6 to 6.7 grains per gallon), drawn from multiple sources including lake huron primary water supply system and municipal well systems. Figure from City of London - 2024 Water Summary Annual Report, last checked 2026-07-03.
Do I need a water softener in London?
Probably not. London water is moderately hard, so most homes get by without one. A simple test kit settles it if you are unsure.
How does London compare with nearby towns?
Closest verified figures: Renfrew at 64.2-144 mg/L mg/L, Bluewater at 107 mg/L, LaSalle at 90 to 125 mg/L as CaCO3 mg/L. London sits at 96-115 mg/L as CaCO3 mg/L, all measured as calcium carbonate.
Source
Source: City of London - 2024 Water Summary Annual Report, last checked 2026-07-03. Hardness varies by neighbourhood, season, and which well or plant serves your street, especially on groundwater systems. These are the municipal published figures as of the verified date, good for planning, not a substitute for a home test or your utility's current report.
Compare nearby verified figures: Renfrew (64.2-144 mg/L mg/L), Bluewater (107 mg/L), LaSalle (90 to 125 mg/L as CaCO3 mg/L). Or see every municipality.