How hard is the water in Rancho Cucamonga, CA?

Tap water hardness
68mg/L
4.0gpg
Moderately hardReports range 36–96

Reported by San Gabriel Valley WC - Fontana · 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 Rancho Cucamonga carries roughly 68 mg/L of dissolved calcium and magnesium, or 4.0 grains per gallon. That is moderately hard water. The number comes from San Gabriel Valley WC - Fontana, dated September 2025. Reports for this system disagree, with values from 36 to 96 mg/L.

Rancho Cucamonga on the hardness scale, with nearby cities
060120180240300360+CA typical 121Rialto: 89 mg/LRialto 89Fontana: 92 mg/LFontana 92Bloomington: 96 mg/LBloomington 96Ontario: 104 mg/LOntario 104Eastvale: 114 mg/LEastvale 114Jurupa Valley: 122 mg/LJurupa Valley 122Upland: 126 mg/LUpland 126Claremont: 157 mg/LClaremont 157Montclair: 166 mg/LMontclair 166La Verne: 231 mg/LLa Verne 231Rancho Cucamonga 68mg/L as calcium carbonate060120180240300360+CA 121Rialto: 89 mg/LRialto 89Fontana: 92 mg/LFontana 92Ontario: 104 mg/LOntario 104Upland: 126 mg/LUpland 126Claremont: 157 mg/LClaremont 157Montclair: 166 mg/LMontclair 16668 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 68 mg/L, Rancho Cucamonga is 53 mg/L below the typical California figure of 121. None of the 10 nearest cities we track has softer water. The range nearby runs from 89 mg/L in Rialto to 231 in La Verne.

What 68 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 Rancho Cucamonga

3 people × 75 gallons a day × 4.0 gpg = 898 grains a day. A 24,000-grain unit regenerates about every 26 days.

Size it for your household

EPA record for Rancho Cucamonga's water system

San Gabriel Valley WC - Fontana · PWSID CA3610041

No health-based violations since 2016

Serves about 228,270 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

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

Somewhat. It measures about 68 mg/L (4.0 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Rancho Cucamonga in grains per gallon?

About 4.0 gpg. One grain per gallon equals 17.1 mg/L, so 68 mg/L divided by 17.1 gives 4.0.

What size water softener do I need in Rancho Cucamonga?

For 3 people using 75 gallons each per day, 4.0 gpg works out to about 898 grains a day. A 24,000-grain softener covers that with a regeneration about every 26 days.

Has the Rancho Cucamonga water system had EPA violations?

EPA records show no health-based violations for San Gabriel Valley WC - Fontana since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, September 23, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.