Water hardness in San Dimas
16.4 gpg very hard
Tap water in San Dimas is very hard: 16.4 gpg (280 mg/L · 15.7 °dH · 28 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA1910142 (2025-09) · data checked 2026-10-19
Range across supply zones: 228–354 mg/L.
The figure is for Golden State Water Company in San Dimas, from State Water Resources Control Board lab results. The median of 9 results from 2021 to 2025, taken at 6 well points, is 280 mg/L as CaCO3 (16.4 gpg), with a range of 228 to 354 mg/L. This is very hard water. Scale builds fast, and a softener is worth considering.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 16.4 gpg |
|---|---|
| Utility | Gswc-San Dimas |
How San Dimas compares
- Tap water in San Dimas is 81 % harder than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 288 of 1372 in the United States (1 = hardest); 78 % of these cities have softer water.
- In California it is number 51 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Glendora, 5 km away (8.2 gpg).
- Nearest city with clearly harder water: Monterey Park, 31 km away (22.2 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Severe scale: heater elements and washing-machine heaters fail early.
- Detergent use is very high; taps and screens coat within days.
- Dishwasher at maximum salt setting.
- An ion-exchange softener is practically essential; RO for drinking water.
How much salt will you use for softening?
Yes. At this hardness a softener pays for itself through appliance life and detergent.
Descale a coffee machine or kettle about every 1 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in San Dimas
| Brand | Setting for this water |
|---|---|
| Bosch | H04 |
| Miele | 16 °dH |
| AEG / Electrolux | 4 |
| Beko | 4th |
| Hoover | S2 |
| LG | H3 |
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 San Dimas water hard or soft?
It is very hard: 280 mg/L as CaCO₃ (16.4 gpg, 15.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in San Dimas 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 San Dimas water?
16.4 gpg, equal to 15.7 °dH, 28 °fH or 280 mg/L calcium carbonate.
What dishwasher salt setting should I use in San Dimas?
For 280 mg/L (15.7 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in San Dimas?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA1910142 (2025-09). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA1910142 · Outdated figure? Tell us