How hard is the water in Oakley, CA?

Tap water hardness
89mg/L
5.2gpg
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 Oakley has about 89 mg/L of hardness, which is 5.2 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Contra Costa Water District, dated October 2025.

Oakley on the hardness scale, with nearby cities
060120180240300360+CA typical 121Blackhawk: 34 mg/LBlackhawk 34Rio Vista: 49 mg/LRio Vista 49Mountain House: 61 mg/LMountain House 61Antioch: 82 mg/LAntioch 82Pittsburg: 82 mg/LPittsburg 82Brentwood: 86 mg/LBrentwood 86Clayton: 86 mg/LClayton 86Concord: 86 mg/LConcord 86Bay Point: 88 mg/LBay Point 88Discovery Bay: 137 mg/LDiscovery Bay 137Oakley 89mg/L as calcium carbonate060120180240300360+CA 121Rio Vista: 49 mg/LRio Vista 49Antioch: 82 mg/LAntioch 82Pittsburg: 82 mg/LPittsburg 82Brentwood: 86 mg/LBrentwood 86Clayton: 86 mg/LClayton 86Discovery Bay: 137 mg/LDiscovery. 13789 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

Oakley sits 32 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 9 have softer water and 1 has harder. The range nearby runs from 34 mg/L in Blackhawk to 137 in Discovery Bay.

What 89 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 Oakley

3 people × 75 gallons a day × 5.2 gpg = 1,174 grains a day. A 24,000-grain unit regenerates about every 20 days.

Size it for your household

EPA record for Oakley's water system

Contra Costa Water District · PWSID CA0710003

No health-based violations since 2016

Serves about 210,500 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

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

Somewhat. It measures about 89 mg/L (5.2 grains per gallon), which the USGS classes as moderately hard.

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

About 5.2 gpg. One grain per gallon equals 17.1 mg/L, so 89 mg/L divided by 17.1 gives 5.2.

What size water softener do I need in Oakley?

For 3 people using 75 gallons each per day, 5.2 gpg works out to about 1,174 grains a day. A 24,000-grain softener covers that with a regeneration about every 20 days.

Has the Oakley water system had EPA violations?

EPA records show no health-based violations for Contra Costa Water District 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.