How hard is the water in Rohnert Park, CA?

Tap water hardness
106mg/L
6.2gpg
Moderately hard

Reported by Rohnert Park, City of · September 2025

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

Rohnert Park water measures 106 mg/L (6.2 gpg) of hardness, moderately hard by USGS standards. The number comes from Rohnert Park, City of, dated September 2025.

Rohnert Park on the hardness scale, with nearby cities
060120180240300360+CA typical 121Napa: 54 mg/LNapa 54Boyes Hot Springs: 62 mg/LBoyes Hot Springs 62Novato: 63 mg/LNovato 63Sonoma: 84 mg/LSonoma 84Healdsburg: 93 mg/LHealdsburg 93Petaluma: 105 mg/LPetaluma 105Cotati: 106 mg/LCotati 106Windsor: 120 mg/LWindsor 120Santa Rosa: 121 mg/LSanta Rosa 121Sebastopol: 142 mg/LSebastopol 142Rohnert Park 106mg/L as calcium carbonate060120180240300360+CA 121Boyes Hot Springs: 62 mg/LBoyes Hot. 62Sonoma: 84 mg/LSonoma 84Petaluma: 105 mg/LPetaluma 105Cotati: 106 mg/LCotati 106Santa Rosa: 121 mg/LSanta Rosa 121Sebastopol: 142 mg/LSebastopol 142106 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 106 mg/L, Rohnert Park is 15 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 6 have softer water and 3 have harder. The range nearby runs from 54 mg/L in Napa to 142 in Sebastopol.

What 106 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 Rohnert Park

3 people × 75 gallons a day × 6.2 gpg = 1,395 grains a day. A 24,000-grain unit regenerates about every 17 days.

Size it for your household

EPA record for Rohnert Park's water system

Rohnert Park, City of · PWSID CA4910014

No health-based violations since 2016

Serves about 43,821 people from groundwater.

Health-based
0
Monitoring or reporting
276
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 Rohnert Park water hard?

Somewhat. It measures about 106 mg/L (6.2 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Rohnert Park in grains per gallon?

About 6.2 gpg. One grain per gallon equals 17.1 mg/L, so 106 mg/L divided by 17.1 gives 6.2.

What size water softener do I need in Rohnert Park?

For 3 people using 75 gallons each per day, 6.2 gpg works out to about 1,395 grains a day. A 24,000-grain softener covers that with a regeneration about every 17 days.

Has the Rohnert Park water system had EPA violations?

EPA records show no health-based violations for Rohnert Park, City of since 2016. There were also 276 monitoring or reporting violations, which are about late or missing tests and notices.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, September 16, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.