Water hardness in Ontario (California)
8.2 gpg hard
Tap water in Ontario (California) is hard: 8.2 gpg (140 mg/L · 7.8 °dH · 14 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA3610034 (2024-12) · data checked 2026-10-19
Range across supply zones: 119–172 mg/L.
The Ontario figure comes from State Water Resources Control Board lab results for Ontario Municipal Utilities Company. The median of 20 results from 2023 and 2024 is 140 mg/L as CaCO3 (8.2 gpg), with a range of 119 to 172 mg/L. The sampling points are listed as wells. This is hard water, so scale on kettles and water heaters is likely. A newer utility report may give a different figure.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 8.2 gpg |
|---|---|
| Utility | Ontario Municipal Utilities Company |
How Ontario (California) compares
- Tap water in Ontario (California) is 10 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 760 of 1372 in the United States (1 = hardest); 43 % of these cities have softer water.
- In California it is number 202 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Moreno Valley, 36 km away (5.1 gpg).
- Nearest city with clearly harder water: Chino, 8 km away (12.3 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 | 3rd |
| 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: 140 mg/L as CaCO₃ (8.2 gpg, 7.8 °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?
8.2 gpg, equal to 7.8 °dH, 14 °fH or 140 mg/L calcium carbonate.
What dishwasher salt setting should I use in Ontario (California)?
For 140 mg/L (7.8 °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: California SWRCB Division of Drinking Water, EDT lab results, system CA3610034 (2024-12). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA3610034 · Outdated figure? Tell us