Hard water in Montclair, CA
Reported by Monte Vista CWD · March 2023
- CA typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in Montclair carries roughly 166 mg/L of dissolved calcium and magnesium, or 9.7 grains per gallon. That is hard water. The number comes from Monte Vista CWD, dated March 2023. Reports for this system disagree, with values from 166 to 220 mg/L.
Montclair sits 45 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 68 mg/L in Rancho Cucamonga to 275 in San Dimas.
What 166 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 166 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 × 9.7 gpg = 2,185 grains a day. A 24,000-grain unit regenerates about every 10 days.
EPA record for Montclair's water system
No health-based violations since 2016
Serves about 56,390 people from surface water.
- 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 Montclair water hard?
Yes. It measures about 166 mg/L (9.7 grains per gallon), which the USGS classes as hard.
What is the water hardness in Montclair in grains per gallon?
About 9.7 gpg. One grain per gallon equals 17.1 mg/L, so 166 mg/L divided by 17.1 gives 9.7.
What size water softener do I need in Montclair?
For 3 people using 75 gallons each per day, 9.7 gpg works out to about 2,185 grains a day. A 24,000-grain softener covers that with a regeneration about every 10 days.
Has the Montclair water system had EPA violations?
EPA records show no health-based violations for Monte Vista WD since 2016.
Nearby cities
- Pomona138 mg/LHard
- Upland126 mg/LHard
- Claremont157 mg/LHard
- La Verne231 mg/LVery hard
- Ontario104 mg/LModerately hard
- San Dimas275 mg/LVery hard
- Diamond Bar153 mg/LHard
- Rancho Cucamonga68 mg/LModerately hard
- Chino Hills81 mg/LModerately hard
- Charter Oak275 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (utility report, March 30, 2023), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.