Hard water in Sebastopol, CA
Reported by Sebastopol, City of · September 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
Sebastopol water measures 142 mg/L (8.3 gpg) of hardness, hard by USGS standards. The number comes from Sebastopol, City of, dated September 2025.
At 142 mg/L, Sebastopol is 21 mg/L above the typical California figure of 121. None of the 10 nearest cities we track has harder water. The range nearby runs from 62 mg/L in Boyes Hot Springs to 121 in Santa Rosa.
What 142 mg/L means at home
Expect white crust on faucets and showerheads, plus spots on dishes that come out of the dishwasher.
Kettles collect scale quickly. Water heaters build up sediment at the bottom of the tank, which makes them work harder over time.
Soap and detergent need a little more to lather, and soap scum shows up in the tub.
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
At 142 mg/L most of the trouble is scale, and only a few things deal with it.
Ion-exchange water softener
The standard whole-house fix. It swaps calcium and magnesium for sodium or potassium and needs salt plus a drain. Size it with the calculator below.
Salt-free conditioner
No salt and no drain line. It changes how minerals form scale instead of removing them, so water still tests hard.
Reverse osmosis or carbon filter
Under-sink reverse osmosis removes minerals from drinking water only. Plain carbon filters improve taste but do not soften.
3 people × 75 gallons a day × 8.3 gpg = 1,868 grains a day. A 24,000-grain unit regenerates about every 12 days.
EPA record for Sebastopol's water system
No health-based violations since 2016
Serves about 7,522 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 Sebastopol water hard?
Yes. It measures about 142 mg/L (8.3 grains per gallon), which the USGS classes as hard.
What is the water hardness in Sebastopol in grains per gallon?
About 8.3 gpg. One grain per gallon equals 17.1 mg/L, so 142 mg/L divided by 17.1 gives 8.3.
What size water softener do I need in Sebastopol?
For 3 people using 75 gallons each per day, 8.3 gpg works out to about 1,868 grains a day. A 24,000-grain softener covers that with a regeneration about every 12 days.
Has the Sebastopol water system had EPA violations?
EPA records show no health-based violations for Sebastopol, City of since 2016.
Nearby cities
- Santa Rosa121 mg/LHard
- Rohnert Park106 mg/LModerately hard
- Cotati106 mg/LModerately hard
- Windsor120 mg/LModerately hard
- Petaluma105 mg/LModerately hard
- Healdsburg93 mg/LModerately hard
- Boyes Hot Springs62 mg/LModerately hard
- Sonoma84 mg/LModerately hard
- Novato63 mg/LModerately hard
- Lucas Valley-Marinwood63 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (utility report, September 14, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.