Castro Valley, CA water hardness

Tap water hardness
34mg/L
2.0gpg
SoftReports range 16–34

Reported by East Bay MUD · October 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Data
Utility report

Castro Valley water measures 34 mg/L (2.0 gpg) of hardness, soft by USGS standards. The number comes from East Bay MUD, dated October 2025. Reports for this system disagree, with values from 16 to 34 mg/L.

Castro Valley on the hardness scale, with nearby cities
060120180240300360+CA typical 121Fairview: 33 mg/LFairview 33Cherryland: 33 mg/LCherryland 33Ashland: 33 mg/LAshland 33San Lorenzo: 33 mg/LSan Lorenzo 33San Leandro: 34 mg/LSan Leandro 34Danville: 34 mg/LDanville 34Oakland: 34 mg/LOakland 34Hayward: 44 mg/LHayward 44San Ramon: 44 mg/LSan Ramon 44Union City: 65 mg/LUnion City 65Castro Valley 34mg/L as calcium carbonate060120180240300360+CA 121Fairview: 33 mg/LFairview 33Cherryland: 33 mg/LCherryland 33Ashland: 33 mg/LAshland 33San Lorenzo: 33 mg/LSan Lorenzo 33San Leandro: 34 mg/LSan Leandro 34Hayward: 44 mg/LHayward 4434 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 34 mg/L, Castro Valley is 87 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 4 have softer water and 3 have harder. The range nearby runs from 33 mg/L in Fairview to 65 in Union City.

What 34 mg/L means at home

Soap and shampoo lather with very little product. Kettles and showerheads stay mostly free of white crust.

Some people notice that soap feels slow to rinse off in soft water. That slippery feel is normal and harmless.

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

Nothing, as far as hardness goes. At 34 mg/L a softener would have almost nothing to remove.

Carbon filter

If the water tastes of chlorine, a pitcher or faucet carbon filter takes care of that. It does not change hardness.

EPA record for Castro Valley's water system

East Bay MUD · PWSID CA0110005

No health-based violations since 2016

Serves about 1,468,000 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

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

No. It measures about 34 mg/L (2.0 grains per gallon), which the USGS classes as soft.

What is the water hardness in Castro Valley in grains per gallon?

About 2.0 gpg. One grain per gallon equals 17.1 mg/L, so 34 mg/L divided by 17.1 gives 2.0.

Has the Castro Valley water system had EPA violations?

EPA records show no health-based violations for East Bay MUD since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, October 13, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.