How hard is the water in Duarte, CA?

Tap water hardness
75mg/L
4.4gpg
Moderately hard

Reported by Cal-Am Water Company - Duarte · July 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

The water in Duarte carries roughly 75 mg/L of dissolved calcium and magnesium, or 4.4 grains per gallon. That is moderately hard water. The number comes from Cal-Am Water Company - Duarte, dated July 2025.

Duarte on the hardness scale, with nearby cities
060120180240300360+CA typical 121Arcadia: 54 mg/LArcadia 54South Monrovia Island: 75 mg/LSouth Monrovia Island 75Vincent: 112 mg/LVincent 112Citrus: 112 mg/LCitrus 112Azusa: 116 mg/LAzusa 116Glendora: 122 mg/LGlendora 122Monrovia: 135 mg/LMonrovia 135Mayflower Village: 135 mg/LMayflower Village 135Sierra Madre: 161 mg/LSierra Madre 161Covina: 167 mg/LCovina 167Duarte 75mg/L as calcium carbonate060120180240300360+CA 121South Monrovia Island: 75 mg/LSouth Monr. 75Vincent: 112 mg/LVincent 112Citrus: 112 mg/LCitrus 112Azusa: 116 mg/LAzusa 116Monrovia: 135 mg/LMonrovia 135Mayflower Village: 135 mg/LMayflower. 13575 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Duarte sits 46 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 1 has softer water and 8 have harder. The range nearby runs from 54 mg/L in Arcadia to 167 in Covina.

What 75 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

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

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for Duarte

3 people × 75 gallons a day × 4.4 gpg = 983 grains a day. A 24,000-grain unit regenerates about every 24 days.

Size it for your household

EPA record for Duarte's water system

Cal-Am Water Company - Duarte · PWSID CA1910186

No health-based violations since 2016

Serves about 24,767 people from groundwater.

Health-based
0
Monitoring or reporting
0
Open now
0

TapWaterData ties Duarte to this system. EPA's service-area records do not name Duarte, 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 Duarte water hard?

Somewhat. It measures about 75 mg/L (4.4 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Duarte in grains per gallon?

About 4.4 gpg. One grain per gallon equals 17.1 mg/L, so 75 mg/L divided by 17.1 gives 4.4.

What size water softener do I need in Duarte?

For 3 people using 75 gallons each per day, 4.4 gpg works out to about 983 grains a day. A 24,000-grain softener covers that with a regeneration about every 24 days.

Has the Duarte water system had EPA violations?

EPA records show no health-based violations for Cal-Am Water Company - Duarte since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, July 8, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.