Water hardness in St. Thomas
117 mg/L moderately hard
Tap water in St. Thomas is moderately hard: 117 mg/L (6.8 gpg · 6.5 °dH · 11.7 °fH).
Source: Ontario Ministry of the Environment, Conservation and Parks, Drinking Water Surveillance Program, Open Government Licence – Ontario (2015) · data checked 2026-10-21
Range across supply zones: 113–121 mg/L.
This figure is over 3 years old; hardness may have changed.
St. Thomas receives Lake Erie water through the Elgin Area Primary Water Supply System. The programme reported 116.5 mg/L as CaCO3 for 2015, ranging from 113 to 121. The data is several years old. Moderate scale on kettles is typical.
Health Canada: hardness above 200 mg/L is considered poor but tolerable; above 500 mg/L unacceptable.
Water data
| Total hardness | 117 mg/L |
|---|---|
| Utility | Elgin Area Primary Water Supply System |
How St. Thomas compares
- Tap water in St. Thomas is 15 % harder than the median of the 254 cities we track in Canada (101 mg/L).
- By hardness it ranks 116 of 254 in Canada (1 = hardest); 55 % of these cities have softer water.
- In Ontario it is number 77 of 120 cities; the regional median is 124 mg/L.
- Nearest city with clearly harder water: Dorchester, 25 km away (265 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 St. Thomas
| 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 St. Thomas water hard or soft?
It is moderately hard: 117 mg/L as CaCO₃ (6.8 gpg, 6.5 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in St. Thomas 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 St. Thomas water?
6.8 gpg, equal to 6.5 °dH, 11.7 °fH or 117 mg/L calcium carbonate.
What dishwasher salt setting should I use in St. Thomas?
For 117 mg/L (6.5 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in St. Thomas?
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 (2015). 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