Water hardness in Cornwall
120 mg/L moderately hard
Tap water in Cornwall is moderately hard: 120 mg/L (7 gpg · 6.7 °dH · 11.9 °fH).
Source: Ontario Ministry of the Environment, Conservation and Parks, Drinking Water Surveillance Program, Open Government Licence – Ontario (2016) · data checked 2026-10-21
Range across supply zones: 119–120 mg/L.
This figure is over 3 years old; hardness may have changed.
Cornwall takes its water from the St. Lawrence River. The programme reported 119.5 mg/L as CaCO3 for 2016, ranging from 119 to 120. The reading is stable. Mild to moderate scale on heating elements is expected.
Health Canada: hardness above 200 mg/L is considered poor but tolerable; above 500 mg/L unacceptable.
Water data
| Total hardness | 120 mg/L |
|---|---|
| Utility | Cornwall Drinking Water System |
How Cornwall compares
- Tap water in Cornwall is 18 % harder than the median of the 254 cities we track in Canada (101 mg/L).
- By hardness it ranks 112 of 254 in Canada (1 = hardest); 56 % of these cities have softer water.
- In Ontario it is number 73 of 120 cities; the regional median is 124 mg/L.
- Nearest city with clearly softer water: Hawkesbury, 65 km away (65 mg/L).
Ranking of the hardest and softest water in Canada →
What it means at home
- Visible kettle scale every few weeks; vinegar or citric acid is enough.
- Water heater and washing machine: some long-term scale; a scale inhibitor slows it.
- Dishwasher: medium salt setting.
- Softener optional; pays off mainly with a gas boiler or tankless heater.
How much salt will you use for softening?
Optional. A scale inhibitor or a small softener protects the heater; soap savings are modest.
Descale a coffee machine or kettle about every 3 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Cornwall
| Brand | Setting for this water |
|---|---|
| Bosch | H01 |
| Miele | 7 °dH |
| AEG / Electrolux | 2 |
| Beko | 2nd |
| Hoover | S1 |
| LG | H1 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Cornwall water hard or soft?
It is moderately hard: 120 mg/L as CaCO₃ (7 gpg, 6.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Cornwall safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. Health Canada: hardness above 200 mg/L is considered poor but tolerable; above 500 mg/L unacceptable.
How many grains per gallon is Cornwall water?
7 gpg, equal to 6.7 °dH, 11.9 °fH or 120 mg/L calcium carbonate.
What dishwasher salt setting should I use in Cornwall?
For 120 mg/L (6.7 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Cornwall?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: Ontario Ministry of the Environment, Conservation and Parks, Drinking Water Surveillance Program, Open Government Licence – Ontario (2016). Method: figure published by the water supplier. Ontario Ministry of the Environment, Conservation and Parks, Drinking Water Surveillance Program, Open Government Licence – Ontario · Outdated figure? Tell us