Water hardness in Petaluma
9.5 gpg hard
Tap water in Petaluma is hard: 9.5 gpg (162 mg/L · 9.1 °dH · 16.2 °fH).
Source: California SWRCB Division of Drinking Water, EDT lab results, system CA4910006 (2025-03) · data checked 2026-10-19
Range across supply zones: 89–269 mg/L.
The Petaluma figure comes from State Water Resources Control Board lab results for the City of Petaluma system. The median of 21 results from 2021 to 2025, taken at 11 well points, is 162 mg/L as CaCO3 (9.5 gpg), with a range of 89 to 269 mg/L. That is hard water, and it varies by well. Expect visible scale on kettles and shower screens.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 9.5 gpg |
|---|---|
| Utility | Petaluma, City Of |
How Petaluma compares
- Tap water in Petaluma is close to the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 653 of 1372 in the United States (1 = hardest); 52 % of these cities have softer water.
- In California it is number 167 of 336 cities; the regional median is 9.5 gpg.
- Nearest city with clearly softer water: Cotati, 12 km away (6.4 gpg).
- Nearest city with clearly harder water: South San Francisco, 68 km away (13 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 Petaluma
| Brand | Setting for this water |
|---|---|
| Bosch | H02 |
| Miele | 9 °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 Petaluma water hard or soft?
It is hard: 162 mg/L as CaCO₃ (9.5 gpg, 9.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Petaluma 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 Petaluma water?
9.5 gpg, equal to 9.1 °dH, 16.2 °fH or 162 mg/L calcium carbonate.
What dishwasher salt setting should I use in Petaluma?
For 162 mg/L (9.1 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in Petaluma?
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 CA4910006 (2025-03). Method: own measurement. California SWRCB Division of Drinking Water, EDT lab results, system CA4910006 · Outdated figure? Tell us