How hard is the water in Antioch, CA?

Tap water hardness
82mg/L
4.8gpg
Moderately hard

Reported by Contra Costa Water District · October 2025

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

Tap water in Antioch has about 82 mg/L of hardness, which is 4.8 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Contra Costa Water District, dated October 2025.

Antioch on the hardness scale, with nearby cities
060120180240300360+CA typical 121Blackhawk: 34 mg/LBlackhawk 34Camino Tassajara: 34 mg/LCamino Tassajara 34Walnut Creek: 40 mg/LWalnut Creek 40Pittsburg: 82 mg/LPittsburg 82Brentwood: 86 mg/LBrentwood 86Clayton: 86 mg/LClayton 86Concord: 86 mg/LConcord 86Bay Point: 88 mg/LBay Point 88Oakley: 89 mg/LOakley 89Discovery Bay: 137 mg/LDiscovery Bay 137Antioch 82mg/L as calcium carbonate060120180240300360+CA 121Pittsburg: 82 mg/LPittsburg 82Brentwood: 86 mg/LBrentwood 86Clayton: 86 mg/LClayton 86Concord: 86 mg/LConcord 86Bay Point: 88 mg/LBay Point 88Oakley: 89 mg/LOakley 8982 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Antioch sits 39 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 3 have softer water and 6 have harder. The range nearby runs from 34 mg/L in Blackhawk to 137 in Discovery Bay.

What 82 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 Antioch

3 people × 75 gallons a day × 4.8 gpg = 1,080 grains a day. A 24,000-grain unit regenerates about every 22 days.

Size it for your household

EPA record for Antioch's water system

City of Antioch · PWSID CA0710001

No health-based violations since 2016

Serves about 116,781 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

EPA lists City of Antioch as the system serving Antioch. The hardness figure above comes from a different system's report, which TapWaterData uses for Antioch.

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 Antioch water hard?

Somewhat. It measures about 82 mg/L (4.8 grains per gallon), which the USGS classes as moderately hard.

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

About 4.8 gpg. One grain per gallon equals 17.1 mg/L, so 82 mg/L divided by 17.1 gives 4.8.

What size water softener do I need in Antioch?

For 3 people using 75 gallons each per day, 4.8 gpg works out to about 1,080 grains a day. A 24,000-grain softener covers that with a regeneration about every 22 days.

Has the Antioch water system had EPA violations?

EPA records show no health-based violations for City of Antioch since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, October 1, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.