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London's tap water comes from two Great Lakes. According to the City of London, about 85% comes from Lake Huron and the rest from Lake Erie, which reaches parts of the south end of the city. Both supplies are run by Huron Erie Water, formerly the Lake Huron and Elgin Area Primary Water Supply Systems, which test hardness once a year. In 2026, treated water measured 106 mg/L at the Lake Huron plant and 118 mg/L at the Elgin Area plant on Lake Erie. That is moderately hard, under the 120 mg/L line, and above Ontario's operational guideline of 80 to 100 mg/L.
Data last reviewed October 24, 2026.
London ranks #14 hardest of 31 cities in the Canadian Hard Water Report 2026. See the full ranking
In other units
Source: Huron Erie Water (Lake Huron and Elgin Area water supply systems), Lake Huron Primary Water Supply System, 2026 first quarter water quality report (PDF). Data for: First quarter 2026, annual test of treated water. Checked October 24, 2026.
In other units
Source: Huron Erie Water (Lake Huron and Elgin Area water supply systems), Elgin Area Primary Water Supply System, 2026 first quarter water quality report (PDF). Data for: First quarter 2026, annual test of treated water. Checked October 24, 2026.
Some scale builds up over time, mostly where water gets heated: kettles, coffee makers and washers. A monthly clean keeps it in check.
At this hardness, grease and detergent residue are the bigger issue, so start with the dishwasher.
Only dishwashers with a built-in water softener have a hardness setting. Here is the setting for this water, worked out from each maker's own table.
| Brand | Lake Huron supply | Elgin Area supply, Lake Erie |
|---|---|---|
| Bosch and ThermadorCanadian models with a softener. H:00 is off. | H:00 | H:01 |
| GaggenauSame ranges as Bosch. The display shows the °E band. | 0-8 | 9-10 |
| MieleSet in °dH. Below 5, Miele says no salt is needed. | 6 | 7 |
| Fisher & PaykelDishDrawer models with a softener. 0 is off. | 1 | 1 |
Most North American dishwashers, including Bosch models sold in the United States, have no water softener and no hardness setting. With those, use rinse aid and run a dishwasher cleaner once a month.
Sources: Bosch SHX78CC5UC manual, Thermador DWHD661EFP manual, Gaggenau DF481701 manual, Miele dishwasher manual (Canada), Fisher & Paykel DishDrawer guide
Softeners take hardness in US grains per gallon: the figure in mg/L divided by 17.12, rounded up.
| Brand | Lake Huron supply | Elgin Area supply, Lake Erie |
|---|---|---|
| Nespresso Essenza PlusHardness level, and cups between descalings | Level 1 (3,000 cups) | Level 1 (3,000 cups) |
| Jura E8Hardness setting | 6 °dH | 7 °dH |
Sources: Nespresso Essenza Plus manual, Jura E8 manual, Breville Barista Touch manual, De'Longhi descaling FAQ, Keurig descaling page
Hard water leaves scale on the heating element and the drum, and more detergent residue behind.
Dissolves grease, detergent residue and limescale buildup, and removes odour-causing buildup.
Clears grease, limescale and odour buildup
Breaks down residue and odour-causing buildup inside your washer.
Removes odour and buildup from the drum and hoses
Removes limescale, mineral buildup and coffee oils inside your coffee maker.
Descales for better-tasting coffee
We use the U.S. Geological Survey scale, in mg/L as CaCO₃.
Utilities usually report hardness in mg/L as calcium carbonate (CaCO₃), which is the same as ppm. Dishwasher and softener manuals often use grains per gallon or German degrees instead. Here is how they convert:
Moderately hard. Huron Erie Water's 2026 tests measured 106 mg/L at the Lake Huron plant and 118 mg/L at the Elgin Area plant on Lake Erie, both under the 120 mg/L line for hard water.
Most of London gets Lake Huron water. About 15% of the city's supply comes from Lake Erie through the Elgin Area system, and the City says it reaches parts of the south end. The two are close in hardness: 106 and 118 mg/L.
For dishwashers with a built-in water softener, each maker's table gives: Lake Huron supply (most of London): Bosch and Thermador H:00, Gaggenau 0-8, Miele 6, Fisher & Paykel 1. Elgin Area supply, Lake Erie (parts of south London): Bosch and Thermador H:01, Gaggenau 9-10, Miele 7, Fisher & Paykel 1. Most North American dishwashers, including Bosch models sold in the United States, have no water softener and no hardness setting. With those, use rinse aid and run a dishwasher cleaner once a month.
Lake Huron supply (most of London): 7 grains per US gallon (rounded up). Elgin Area supply, Lake Erie (parts of south London): 7 grains per US gallon (rounded up).
Lake Huron supply (most of London): 6.2 grains per US gallon, or 7.4 grains per imperial gallon. Elgin Area supply, Lake Erie (parts of south London): 6.9 grains per US gallon, or 8.3 grains per imperial gallon.
Huron Erie Water (Lake Huron and Elgin Area water supply systems), Lake Huron Primary Water Supply System, 2026 first quarter water quality report (PDF). Data for First quarter 2026, annual test of treated water. Huron Erie Water (Lake Huron and Elgin Area water supply systems), Elgin Area Primary Water Supply System, 2026 first quarter water quality report (PDF). Data for First quarter 2026, annual test of treated water. We update this page when a new report comes out.
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