Hard water in Oak Park, CA
Reported by California Water Service CO - Westlake · October 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Oak Park carries roughly 138 mg/L of dissolved calcium and magnesium, or 8.1 grains per gallon. That is hard water. The number comes from California Water Service CO - Westlake, dated October 2025.
At 138 mg/L, Oak Park is 17 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 6 have softer water and 4 have harder. The range nearby runs from 77 mg/L in Calabasas to 236 in Stevenson Ranch.
What 138 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 138 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 × 8.1 gpg = 1,811 grains a day. A 24,000-grain unit regenerates about every 13 days.
EPA record for Oak Park's water system
No health-based violations since 2016
Serves about 19,544 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 0
- Open now
- 0
TapWaterData ties Oak Park to this system. EPA's service-area records do not name Oak Park, so check the utility printed on your water bill.
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 Oak Park water hard?
Yes. It measures about 138 mg/L (8.1 grains per gallon), which the USGS classes as hard.
What is the water hardness in Oak Park in grains per gallon?
About 8.1 gpg. One grain per gallon equals 17.1 mg/L, so 138 mg/L divided by 17.1 gives 8.1.
What size water softener do I need in Oak Park?
For 3 people using 75 gallons each per day, 8.1 gpg works out to about 1,811 grains a day. A 24,000-grain softener covers that with a regeneration about every 13 days.
Has the Oak Park water system had EPA violations?
EPA records show no health-based violations for California Water Service CO - Westlake since 2016.
Nearby cities
- Agoura Hills88 mg/LModerately hard
- Westlake Village88 mg/LModerately hard
- Simi Valley181 mg/LVery hard
- Thousand Oaks117 mg/LModerately hard
- Calabasas77 mg/LModerately hard
- Moorpark190 mg/LVery hard
- Topanga77 mg/LModerately hard
- Camarillo218 mg/LVery hard
- Fillmore77 mg/LModerately hard
- Stevenson Ranch236 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.