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Ottawa's central water supply comes from the Ottawa River and is treated at two plants, Lemieux Island and Britannia, which use the same process. In 2025, treated water averaged 21.4 mg/L of total hardness at Lemieux Island and 21.1 mg/L at Britannia, according to the City of Ottawa. That is soft water, well under the 60 mg/L line. In Ottawa, scale builds slowly, and grease, detergent residue and odours are a bigger worry than limescale.
Data last reviewed October 24, 2026.
Ottawa is tied for #4 softest of 31 cities in the Canadian Hard Water Report 2026. See the full ranking
In other units
Source: City of Ottawa, Lemieux Island Water Purification Plant, 2025 drinking water quality (PDF). Data for: 2025, treated water average. Checked October 24, 2026.
In other units
Source: City of Ottawa, Britannia Water Purification Plant, 2025 drinking water quality (PDF). Data for: 2025, treated water average. Checked October 24, 2026.
Scale builds slowly with soft water. Odours, grease and detergent residue are the bigger issue, so clean the dishwasher and the washer about every two weeks.
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 | Lemieux Island plant | Britannia plant |
|---|---|---|
| Bosch and ThermadorCanadian models with a softener. H:00 is off. | H:00 | H:00 |
| GaggenauSame ranges as Bosch. The display shows the °E band. | 0-8 | 0-8 |
| MieleSet in °dH. Below 5, Miele says no salt is needed. | 1 | 1 |
| Fisher & PaykelDishDrawer models with a softener. 0 is off. | 0 | 0 |
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 | Lemieux Island plant | Britannia plant |
|---|---|---|
| Nespresso Essenza PlusHardness level, and cups between descalings | Level 0 (4,000 cups) | Level 0 (4,000 cups) |
| Jura E8Hardness setting | 1 °dH | 1 °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
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:
No. The City of Ottawa's 2025 results averaged 21.4 mg/L at the Lemieux Island plant and 21.1 mg/L at Britannia, which is soft water. Water only counts as moderately hard above 60 mg/L.
No. These figures are for the City's central supply from the Ottawa River. Private wells and the City's small communal well systems in some rural villages are not covered here.
Less often than in harder-water cities. Scale builds slowly with soft water. Grease, detergent residue and odours build up in dishwashers and washers whatever your water, so cleaning the dishwasher and the washer about every two weeks still makes sense.
For dishwashers with a built-in water softener, each maker's table gives: Lemieux Island plant: Bosch and Thermador H:00, Gaggenau 0-8, Miele 1, Fisher & Paykel 0. Britannia plant: Bosch and Thermador H:00, Gaggenau 0-8, Miele 1, Fisher & Paykel 0. 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.
Lemieux Island plant: 2 grains per US gallon (rounded up). Britannia plant: 2 grains per US gallon (rounded up).
Lemieux Island plant: 1.3 grains per US gallon, or 1.5 grains per imperial gallon. Britannia plant: 1.2 grains per US gallon, or 1.5 grains per imperial gallon.
City of Ottawa, Lemieux Island Water Purification Plant, 2025 drinking water quality (PDF). Data for 2025, treated water average. City of Ottawa, Britannia Water Purification Plant, 2025 drinking water quality (PDF). Data for 2025, treated water average. We update this page when a new report comes out.
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