Contra Costa County Water Quality: 6 Cities Ranked by the Records
Contra Costa County, California: 6 city reports built from EPA and utility records. A county has many suppliers; each city shows the system that serves it.
Highest result for each contaminant
One row per contaminant: the highest result any system in the county reported, against its limit. Open a row for the systems behind it.
LithiumDetected in 3 systems of 6 tested10 µg/L EPA health reference level (screening, not a legal limit) · US EPAHighest102 µg/L
- BRENTWOOD102 µg/LSample date: 2024-06-24 to 2025-05-07
- TOWN OF DISCOVERY BAY34 µg/LSample date: 2023-02-28 to 2023-10-03
- CITY OF PITTSBURG22.9 µg/LSample date: 2023-07-11 to 2024-04-03
- CITY OF ANTIOCHNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-11-14 to 2024-08-05
- CITY OF MARTINEZNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-07-05 to 2024-04-03
- CONTRA COSTA WATER DISTRICTNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-03-16 to 2023-12-13
Water hardnessDetected in 1 systemAesthetic, no federal health limit · USGSHighest4.3 gpg
- CONTRA COSTA WATER DISTRICT4.3 gpgReporting year: 2025
30 substances tested, none detected in any systemShow
Tested in these 6 systems: BRENTWOOD, CITY OF ANTIOCH, CITY OF MARTINEZ, CITY OF PITTSBURG, CONTRA COSTA WATER DISTRICT, TOWN OF DISCOVERY BAY
- 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS)
- 1H, 1H, 2H, 2H-perfluorodecane sulfonic acid (8:2 FTS)
- 1H, 1H, 2H, 2H-perfluorohexane sulfonic acid (4:2 FTS)
- 1H, 1H, 2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)
- 4,8-Dioxa-3H-perfluorononanoic acid (ADONA)
- 9-Chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS)
- Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals)
- Lead (90th percentile)
- N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)
- N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)
- Nonafluoro-3,6-dioxaheptanoic acid (NFDHA)
- Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA)
- Perfluoro-3-methoxypropanoic acid (PFMPA)
- Perfluoro-4-methoxybutanoic acid (PFMBA)
- Perfluorobutanesulfonic acid (PFBS)
- Perfluorobutanoic acid (PFBA)
- Perfluorodecanoic acid (PFDA)
- Perfluorododecanoic acid (PFDoA)
- Perfluoroheptanesulfonic acid (PFHpS)
- Perfluoroheptanoic acid (PFHpA)
- Perfluorohexanesulfonic acid (PFHxS)
- Perfluorohexanoic acid (PFHxA)
- Perfluorononanoic acid (PFNA)
- Perfluorooctanesulfonic acid (PFOS)
- Perfluorooctanoic acid (PFOA)
- Perfluoropentanesulfonic acid (PFPeS)
- Perfluoropentanoic acid (PFPeA)
- Perfluorotetradecanoic acid (PFTA)
- Perfluorotridecanoic acid (PFTrDA)
- Perfluoroundecanoic acid (PFUnA)
Cities ranked by the records
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Ranked by the Purity Score of each city's main water system, highest first. Scores belong to water systems; there is no county score. The score is computed only from contaminants measured in the published EPA record, so this ranks the record, not which city's water is safest. How the score works.
0of 6 cities above the 15 µg/L action level
Based on each system's 90th-percentile result. Lead from household plumbing isn't in this record.
Lead in California1city reports hardness · Concord, 4.3 gpg
None above 7 gpg, the USGS threshold for hard water. An aesthetic measure with no federal health limit.
Hard water explainedLargest water systems
- ConcordCONTRA COSTA WATER DISTRICT · CA0710003210,500 served
- AntiochCITY OF ANTIOCH · CA0710001116,781 served
- BrentwoodBRENTWOOD · CA071000464,513 served
- PittsburgCITY OF PITTSBURG · CA071000862,500 served
- MartinezCITY OF MARTINEZ · CA071000631,015 served
- Discovery BayTOWN OF DISCOVERY BAY · CA071000916,790 served
Frequently asked
How does Contra Costa County tap water compare across cities?
PurityMap ranks 6 cities in Contra Costa County by the Purity Score of each city's main water system, computed only from contaminants measured in the published EPA record. Scores belong to water systems, not to cities. The highest published score is Concord's main water system: CONTRA COSTA WATER DISTRICT · PWSID CA0710003 · Purity Score 100 (Excellent) · Confidence: moderate · Assessed at the water-system level. The ranking compares the records, not which city's water is safest, and your own tap can differ with household plumbing.
How many Contra Costa County cities had a PFAS sample above a 2024 EPA limit?
None of the 6 Contra Costa County city reports had a PFAS sample above a 2024 EPA limit in EPA's UCMR 5 testing. PFAS were detected below the limit in 0.
Is there lead in Contra Costa County tap water?
Utilities report lead as a 90th-percentile result from home taps. 0 of 6 Contra Costa County cities reported a value above zero, and none was above the 15 µg/L federal action level. Lead usually comes from a building's own pipes and fixtures, so only a test at your tap tells you what you drink.
Does Contra Costa County have hard water?
Hardness is published in utility water-quality reports for 1 Contra Costa County city on record; the hardest is Concord at 4.3 grains per gallon. Hardness affects scale and appliances; it is not a health finding.
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