Hard water in Claremont, CA
Reported by GSWC - Claremont · September 2025
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Claremont carries roughly 157 mg/L of dissolved calcium and magnesium, or 9.2 grains per gallon. That is hard water. The number comes from GSWC - Claremont, dated September 2025. Reports for this system disagree, with values from 88 to 157 mg/L.
Claremont sits 36 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 5 have softer water and 5 have harder. The range nearby runs from 68 mg/L in Rancho Cucamonga to 275 in San Dimas.
What 157 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 157 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 × 9.2 gpg = 2,063 grains a day. A 24,000-grain unit regenerates about every 11 days.
EPA record for Claremont's water system
No health-based violations since 2016
Serves about 39,776 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 0
- Open now
- 0
TapWaterData ties Claremont to this system. EPA's service-area records do not name Claremont, 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 Claremont water hard?
Yes. It measures about 157 mg/L (9.2 grains per gallon), which the USGS classes as hard.
What is the water hardness in Claremont in grains per gallon?
About 9.2 gpg. One grain per gallon equals 17.1 mg/L, so 157 mg/L divided by 17.1 gives 9.2.
What size water softener do I need in Claremont?
For 3 people using 75 gallons each per day, 9.2 gpg works out to about 2,063 grains a day. A 24,000-grain softener covers that with a regeneration about every 11 days.
Has the Claremont water system had EPA violations?
EPA records show no health-based violations for GSWC - Claremont since 2016.
Nearby cities
- Upland126 mg/LHard
- La Verne231 mg/LVery hard
- Montclair166 mg/LHard
- Pomona138 mg/LHard
- San Dimas275 mg/LVery hard
- Glendora122 mg/LHard
- Charter Oak275 mg/LVery hard
- Rancho Cucamonga68 mg/LModerately hard
- Ontario104 mg/LModerately hard
- Covina167 mg/LHard
Hardness data: TapWaterData US Water Hardness (utility report, September 29, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.