Water hardness in Duarte
8.4 gpg hard
Tap water in Duarte is hard: 8.4 gpg (144 mg/L · 8 °dH · 14.3 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA1910186 (2026-02) · data checked 2026-10-19
Range across supply zones: 97–216 mg/L.
The figure is for California American Water in Duarte, from State Water Resources Control Board lab results. The median of 18 results from 2022 to 2026, taken at 10 well points, is 143.5 mg/L as CaCO3 (8.4 gpg), with a range of 97.2 to 216 mg/L. That is hard water, and it varies by well. Expect visible scale on kettles.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 8.4 gpg |
|---|---|
| Utility | Cal-Am Water Company - Duarte |
How Duarte compares
- Tap water in Duarte is 7 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 750 of 1372 in the United States (1 = hardest); 45 % of these cities have softer water.
- In California it is number 198 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: East Pasadena, 12 km away (5.2 gpg).
- Nearest city with clearly harder water: Monrovia, 3 km away (10.8 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 Duarte
| 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 Duarte water hard or soft?
It is hard: 144 mg/L as CaCO₃ (8.4 gpg, 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 Duarte 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 Duarte water?
8.4 gpg, equal to 8 °dH, 14.3 °fH or 144 mg/L calcium carbonate.
What dishwasher salt setting should I use in Duarte?
For 144 mg/L (8 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in Duarte?
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 CA1910186 (2026-02). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA1910186 · Outdated figure? Tell us