How hard is the water in Windsor, CA?

Tap water hardness
120mg/L
7.0gpg
Moderately hardCounty estimate

County estimate from 501 water samples in Sonoma County · July 2026

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

Water samples from around Windsor put hardness at about 120 mg/L (7.0 gpg), which would be moderately hard on the USGS scale. Treat this as a rough guide: it is the median of 501 samples taken across Sonoma County, mostly wells and streams, not a test of Windsor's treated tap water.

Windsor on the hardness scale, with nearby cities
060120180240300360+CA typical 121Napa: 54 mg/LNapa 54Boyes Hot Springs: 62 mg/LBoyes Hot Springs 62Sonoma: 84 mg/LSonoma 84Healdsburg: 93 mg/LHealdsburg 93Clearlake: 96 mg/LClearlake 96Petaluma: 105 mg/LPetaluma 105Rohnert Park: 106 mg/LRohnert Park 106Cotati: 106 mg/LCotati 106Santa Rosa: 121 mg/LSanta Rosa 121Sebastopol: 142 mg/LSebastopol 142Windsor 120mg/L as calcium carbonate060120180240300360+CA 121Healdsburg: 93 mg/LHealdsburg 93Petaluma: 105 mg/LPetaluma 105Rohnert Park: 106 mg/LRohnert Pa. 106Cotati: 106 mg/LCotati 106Santa Rosa: 121 mg/LSanta Rosa 121Sebastopol: 142 mg/LSebastopol 142120 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 120 mg/L, Windsor is close to the typical California figure of 121 mg/L. Of the 10 nearest cities we track, 8 have softer water and 2 have harder. The range nearby runs from 54 mg/L in Napa to 142 in Sebastopol.

What 120 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 Windsor

3 people × 75 gallons a day × 7.0 gpg = 1,580 grains a day. A 24,000-grain unit regenerates about every 15 days.

Size it for your household

EPA record for Windsor's water system

Windsor, Town of · PWSID CA4910017

No health-based violations since 2016

Serves about 25,561 people from groundwater.

Health-based
0
Monitoring or reporting
0
Open now
0

EPA lists this system as serving Windsor.

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 Windsor water hard?

Somewhat. It measures about 120 mg/L (7.0 grains per gallon), which the USGS classes as moderately hard.

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

About 7.0 gpg. One grain per gallon equals 17.1 mg/L, so 120 mg/L divided by 17.1 gives 7.0.

What size water softener do I need in Windsor?

For 3 people using 75 gallons each per day, 7.0 gpg works out to about 1,580 grains a day. A 24,000-grain softener covers that with a regeneration about every 15 days.

Has the Windsor water system had EPA violations?

EPA records show no health-based violations for Windsor, Town of since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (county estimate, July 4, 2026), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.