PFAS in California drinking water

Every California public water system that reported a PFAS detection during EPA UCMR 5 monitoring, how many sit above the 2024 federal limits, and the standard California applies. Concentrations are in nanograms per litre, the same unit as parts per trillion.

This is the United States view of the North American PFAS dataset. The complete dataset, including all 3,452 US systems and 97 Canadian sites, lives on the main PFAS contamination map.

Loading federal sample results

What California requires

Guidance value only

Agency

State Water Resources Control Board (DDW)

Citation

Health and Safety Code notification and response levels; no state MCL adopted

Effective

2025-10-29

California has not adopted a state PFAS MCL. Notification levels are advisory and trigger customer notification, and response levels recommend taking a source out of service. DDW issued new and revised levels for PFOA, PFOS, PFHxS and PFHxA on 29 October 2025. The enforceable drinking water standard in California is the federal rule.

Compound

Limit (ng/L)

Note

PFOA

Notification level; Response 10

PFOS

Notification level; Response 40

PFHxS

Notification level; Response 10

PFHxA

1,000

Notification level; Response 10,000

Citations

California SWRCB DDW, Notification Levels

US EPA PFAS National Primary Drinking Water Regulation (2024)

US EPA UCMR 5 occurrence data

Last reviewed 2026-08-13. Verify against the agency source before making a compliance or remediation decision.

Full California regulatory brief

All US state limits

Where the numbers on this page come from

Every count above is read straight from a published government file. Nothing is modelled, averaged, or estimated. The rules below are the exact rules used to produce the figures for California.

Dataset used for the system counts

Source

US EPA, Fifth Unregulated Contaminant Monitoring Rule (UCMR 5), public occurrence data

File

UCMR5_All.txt, the full public results file released by EPA

Extracted

2026-08-13

Units

Nanograms per litre, equivalent to parts per trillion. EPA publishes micrograms per litre and those values are multiplied by 1,000.

Coverage rules that decide what is counted for California

Who is in UCMR 5. All public water systems serving more than 3,300 people, plus a national sample of 800 smaller systems. Private wells and most small systems are not monitored, so they cannot appear here.

Which systems are listed. Only systems whose state field is CA and that reported at least one measured PFAS detection. Systems that monitored and found nothing are not shown, and their absence is not evidence of contamination.

Systems that cannot be placed. 87 systems nationally reported a detection but have no serviced ZIP code published by EPA, so they carry no location and are excluded from these counts. National totals on the map page include them.

Which value is used. The highest result a system reported for each compound across its sampling events. Results flagged by EPA as non-detects are excluded, as are the lithium results carried in the same file.

The above a limit count. A system is counted when its maximum result for a compound exceeds the 2024 federal Maximum Contaminant Level: 4 ng/L for PFOA and PFOS, 10 ng/L for PFHxS, PFNA, and HFPO-DA.

The Hazard Index count. Calculated with EPA's own mixture method for PFHxS, PFNA, HFPO-DA, and PFBS. A system is counted when the index is above 1.

What monitoring data is not. Exceeding a 2024 limit in this dataset is not a compliance violation. The federal limits carry a 2029 compliance date, which EPA proposed on 18 May 2026 to move to 2031 for PFOA and PFOS in a rule that is not final, and treatment may have been installed since the sample was taken.

If any figure on this page does not match its source file, tell Nelson and it will be corrected or removed.