Water hardness in Ontario (California)
8 gpg hard
Tap water in Ontario (California) is hard: 8 gpg (137 mg/L · 7.7 °dH · 13.7 °fH).
Source: Ontario Municipal Utilities Company - 2025 Consumer Confidence Report (2025) · data checked 2026-10-23
Range across supply zones: 25–220 mg/L.
5 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| gpg | mg/L | ||
|---|---|---|---|
| Imported Water (WFA w/ SAWCO) | 5.3 | 91 | moderately hard |
| Local Groundwater (OMUC wells) | 7.2 | 124 | hard |
| Purchased Groundwater CDA 1 (870 Zone) | 8 | 137 | hard |
| Purchased Groundwater CDA 2 (1110 Zone) | 8.2 | 140 | hard |
| Purchased Groundwater JCSD (870 Zone) | 10.3 | 177 | hard |
Ontario Municipal Utilities Company serves 5 zones from local wells in the Chino Basin, treated desalter water and imported State Water Project supply, in different proportions across the city. That blend explains the wide spread of 25–220 mg/L around 137 mg/L CaCO₃. Ask which zone your address is in; scale on fixtures and water heaters is common in the harder areas.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 8 gpg |
|---|---|
| Utility | Ontario Municipal Utilities Company (OMUC) |
How Ontario (California) compares
- Tap water in Ontario (California) is 12 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 791 of 1372 in the United States (1 = hardest); 42 % of these cities have softer water.
- In California it is number 212 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: East Pasadena, 40 km away (5.2 gpg).
- Nearest city with clearly harder water: Upland, 6 km away (10.2 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Fast scale on taps, shower screens and kettle; white spots on glassware.
- Water heater: efficiency loss and element failures within years if unprotected.
- Dry skin and dull hair after showering are common.
- Softener recommended; jug or reverse osmosis for drinking.
How much salt will you use for softening?
Recommended, especially with a heater or boiler: scale cuts efficiency and shortens its life.
Descale a coffee machine or kettle about every 2 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Ontario
| Brand | Setting for this water |
|---|---|
| Bosch | H01 |
| Miele | 8 °dH |
| AEG / Electrolux | 2 |
| Beko | 2nd |
| Hoover | S1 |
| LG | H2 |
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 Ontario (California) water hard or soft?
It is hard: 137 mg/L as CaCO₃ (8 gpg, 7.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Ontario (California) safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
How many grains per gallon is Ontario (California) water?
8 gpg, equal to 7.7 °dH, 13.7 °fH or 137 mg/L calcium carbonate.
What dishwasher salt setting should I use in Ontario (California)?
For 137 mg/L (7.7 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in Ontario (California)?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Source
Source: Ontario Municipal Utilities Company - 2025 Consumer Confidence Report (2025). Method: figure published by the water supplier. Ontario Municipal Utilities Company - 2025 Consumer Confidence Report · Outdated figure? Tell us