Hard water in Monrovia, CA
Reported by Monrovia-City, Water Dept. · 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 Monrovia carries roughly 135 mg/L of dissolved calcium and magnesium, or 7.9 grains per gallon. That is hard water. The number comes from Monrovia-City, Water Dept., dated September 2025.
Monrovia sits 14 mg/L above the typical California figure of 121. Of the 10 nearest cities we track, 6 have softer water and 3 have harder. The range nearby runs from 54 mg/L in Arcadia to 192 in East Pasadena.
What 135 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 135 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 × 7.9 gpg = 1,780 grains a day. A 24,000-grain unit regenerates about every 13 days.
EPA record for Monrovia's water system
No health-based violations since 2016
Serves about 37,931 people from groundwater.
- 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 Monrovia water hard?
Yes. It measures about 135 mg/L (7.9 grains per gallon), which the USGS classes as hard.
What is the water hardness in Monrovia in grains per gallon?
About 7.9 gpg. One grain per gallon equals 17.1 mg/L, so 135 mg/L divided by 17.1 gives 7.9.
What size water softener do I need in Monrovia?
For 3 people using 75 gallons each per day, 7.9 gpg works out to about 1,780 grains a day. A 24,000-grain softener covers that with a regeneration about every 13 days.
Has the Monrovia water system had EPA violations?
EPA records show no health-based violations for Monrovia-City, Water Dept. since 2016. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- Duarte75 mg/LModerately hard
- South Monrovia Island75 mg/LModerately hard
- Mayflower Village135 mg/LHard
- Arcadia54 mg/LSoft
- Sierra Madre161 mg/LHard
- Azusa116 mg/LModerately hard
- East Pasadena192 mg/LVery hard
- Vincent112 mg/LModerately hard
- Temple City113 mg/LModerately hard
- East San Gabriel192 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (utility report, September 15, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.