How hard is the water in Petaluma, CA?

Tap water hardness
105mg/L
6.1gpg
Moderately hard

Reported by Petaluma, City of · August 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

Tap water in Petaluma has about 105 mg/L of hardness, which is 6.1 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Petaluma, City of, dated August 2025.

Petaluma on the hardness scale, with nearby cities
060120180240300360+CA typical 121Napa: 54 mg/LNapa 54Fairfax: 56 mg/LFairfax 56Boyes Hot Springs: 62 mg/LBoyes Hot Springs 62Novato: 63 mg/LNovato 63Lucas Valley-Marinwood: 63 mg/LLucas Valley-Marinwood 63Sonoma: 84 mg/LSonoma 84Cotati: 106 mg/LCotati 106Rohnert Park: 106 mg/LRohnert Park 106Santa Rosa: 121 mg/LSanta Rosa 121Sebastopol: 142 mg/LSebastopol 142Petaluma 105mg/L as calcium carbonate060120180240300360+CA 121Boyes Hot Springs: 62 mg/LBoyes Hot. 62Novato: 63 mg/LNovato 63Lucas Valley-Marinwood: 63 mg/LLucas Vall. 63Sonoma: 84 mg/LSonoma 84Cotati: 106 mg/LCotati 106Rohnert Park: 106 mg/LRohnert Pa. 106105 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 105 mg/L, Petaluma is 16 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 6 have softer water and 4 have harder. The range nearby runs from 54 mg/L in Napa to 142 in Sebastopol.

What 105 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.

What to do about it

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for Petaluma

3 people × 75 gallons a day × 6.1 gpg = 1,381 grains a day. A 24,000-grain unit regenerates about every 17 days.

Size it for your household

EPA record for Petaluma's water system

Petaluma, City of · PWSID CA4910006

No health-based violations since 2016

Serves about 61,427 people from groundwater.

Health-based
0
Monitoring or reporting
0
Open now
0

Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.

Questions

Is Petaluma water hard?

Somewhat. It measures about 105 mg/L (6.1 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Petaluma in grains per gallon?

About 6.1 gpg. One grain per gallon equals 17.1 mg/L, so 105 mg/L divided by 17.1 gives 6.1.

What size water softener do I need in Petaluma?

For 3 people using 75 gallons each per day, 6.1 gpg works out to about 1,381 grains a day. A 24,000-grain softener covers that with a regeneration about every 17 days.

Has the Petaluma water system had EPA violations?

EPA records show no health-based violations for Petaluma, City of since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, August 25, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.