Hard water in Simi Valley, CA
Reported by Ventura WWD No. 8 - Simi Valley · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
Simi Valley water measures 181 mg/L (10.6 gpg) of hardness, very hard by USGS standards. The number comes from Ventura WWD No. 8 - Simi Valley, dated October 2025. Reports for this system disagree, with values from 181 to 213 mg/L.
At 181 mg/L, Simi Valley is 60 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 77 mg/L in Calabasas to 236 in Stevenson Ranch.
What 181 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 181 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 × 10.6 gpg = 2,380 grains a day. A 24,000-grain unit regenerates about every 10 days.
EPA record for Simi Valley's water system
No health-based violations since 2016
Serves about 94,736 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 1
- 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 Simi Valley water hard?
Yes. It measures about 181 mg/L (10.6 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Simi Valley in grains per gallon?
About 10.6 gpg. One grain per gallon equals 17.1 mg/L, so 181 mg/L divided by 17.1 gives 10.6.
What size water softener do I need in Simi Valley?
For 3 people using 75 gallons each per day, 10.6 gpg works out to about 2,380 grains a day. A 24,000-grain softener covers that with a regeneration about every 10 days.
Has the Simi Valley water system had EPA violations?
EPA records show no health-based violations for Ventura WWD No. 8 - Simi Valley since 2016. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- Oak Park138 mg/LHard
- Moorpark190 mg/LVery hard
- Agoura Hills88 mg/LModerately hard
- Thousand Oaks117 mg/LModerately hard
- Westlake Village88 mg/LModerately hard
- Calabasas77 mg/LModerately hard
- Stevenson Ranch236 mg/LVery hard
- Fillmore77 mg/LModerately hard
- Topanga77 mg/LModerately hard
- Castaic236 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (utility report, October 6, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.