Hard water in San Jose, CA
Reported by San Jose Water · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 1
- Softener for 3 people
- 24k grain
- Data
- Utility report
San Jose water measures 185 mg/L (10.8 gpg) of hardness, very hard by USGS standards. The number comes from San Jose Water, dated October 2025.
San Jose sits 64 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 7 have softer water and 3 have harder. The range nearby runs from 49 mg/L in Milpitas to 298 in Sunnyvale.
What 185 mg/L means at home
Scale forms fast here. Kettles and coffee makers need regular descaling, and showerheads clog unless you clean them.
Tank water heaters collect mineral sediment that insulates the water from the burner, so flushing the tank matters more than usual.
Dishes and glass shower doors spot easily. Soap scum and a dull film on hair or laundry are common complaints.
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 185 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 × 10.8 gpg = 2,430 grains a day. A 24,000-grain unit regenerates about every 9 days.
EPA record for San Jose's water system
1 health-based violation since 2016
Serves about 1,039,920 people from surface water.
- Health-based
- 1
- Monitoring or reporting
- 1
- Open now
- 0
| Contaminant or rule | Violations | Period | Status |
|---|---|---|---|
| Surface Water Treatment Rulefiltration and disinfection | 1 | 2023 | Resolved |
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 San Jose water hard?
Yes. It measures about 185 mg/L (10.8 grains per gallon), which the USGS classes as very hard.
What is the water hardness in San Jose in grains per gallon?
About 10.8 gpg. One grain per gallon equals 17.1 mg/L, so 185 mg/L divided by 17.1 gives 10.8.
What size water softener do I need in San Jose?
For 3 people using 75 gallons each per day, 10.8 gpg works out to about 2,430 grains a day. A 24,000-grain softener covers that with a regeneration about every 9 days.
Has the San Jose water system had EPA violations?
EPA records show 1 health-based violation for San Jose Water since 2016, involving Surface Water Treatment Rule. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- Alum Rock178 mg/LHard
- East Foothills178 mg/LHard
- Campbell178 mg/LHard
- Los Gatos178 mg/LHard
- Santa Clara248 mg/LVery hard
- Milpitas49 mg/LSoft
- Saratoga178 mg/LHard
- Cupertino186 mg/LVery hard
- Sunnyvale298 mg/LVery hard
- Morgan Hill49 mg/LSoft
Hardness data: TapWaterData US Water Hardness (utility report, October 7, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.