PFAS compliance — PFOA, PFOS, and the Hazard Index.
The federal PFAS National Primary Drinking Water Regulation sets individual MCLs for PFOA and PFOS, and a Hazard Index MCL for a four-PFAS mixture (PFHxS, HFPO-DA, PFNA, PFBS). Procedural compliance clauses live in 40 CFR 141 Subpart Z (§§ 141.900–141.905); the numeric MCLs and Health-Based Water Concentrations (HBWCs) are codified in § 141.61(c). Community water systems that detect a PFAS must disclose it in the annual Consumer Confidence Report per § 141.153(d)(4).
Verified against eCFR § 141.61(c) on 2026-04-18.
PFAS MCLs are codified as concentrations in § 141.61(c). Four of the six regulated PFAS do not have individual MCLs — they are regulated through the Hazard Index, a unitless sum of hazard quotients that must be ≤ 1. The Health-Based Water Concentration (HBWC) is the denominator in each component’s hazard quotient.
Hazard Index formula (from § 141.61(c)): HI = ([HFPO-DA]/10) + ([PFBS]/2000) + ([PFNA]/10) + ([PFHxS]/10), with concentrations and HBWCs expressed in ng/L. An HI > 1 indicates the mixture exceeds the MCL.
§§ 141.900–141.905.
Subpart Z governs monitoring, compliance determinations, reporting, and violation classifications. Individual MCL values and HBWCs live in § 141.61(c). This split — numeric limits in Subpart G, procedural rules in Subpart Z — follows the pattern EPA uses for most NPDWR families.
General requirements
Purpose, applicability, and general framework of the PFAS NPDWR. Applies to community water systems and non-transient non-community water systems.
Read on eCFR →Analytical requirements
Approved analytical methods (EPA Methods 533 and 537.1) for PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and PFBS. Minimum reporting levels and laboratory certification.
Read on eCFR →Monitoring requirements
Initial monitoring schedule, routine monitoring, and triggered-monitoring requirements based on detections above trigger levels. Reduced monitoring eligibility.
Read on eCFR →Compliance requirements
Running annual average compliance determinations for each individual PFAS MCL plus Hazard Index compliance for the regulated PFAS mixture (PFHxS, HFPO-DA, PFNA, PFBS).
Read on eCFR →Reporting and recordkeeping requirements
Reporting to primacy agencies, public notification triggers, and record-retention obligations for PFAS monitoring results and compliance determinations.
Read on eCFR →Violations
Types of violations (MCL, monitoring, reporting) and the corresponding public notification tier under Subpart Q.
Read on eCFR →PFAS in your Consumer Confidence Report.
Any PFAS detected at or above the analytical minimum reporting level must be disclosed in the annual Consumer Confidence Report per 40 CFR § 141.153(d)(4). Both the individual concentration and, for the four Hazard Index PFAS, the system’s Hazard Index calculation must be presented. See our Consumer Confidence Report guide for the section-by-section walkthrough, or draft your own on the CCR Agent.
Numeric values in this reference are sourced directly from the eCFR on 2026-04-18. If EPA updates the rule (as has happened with the LCR→LCRI transition), we re-fetch the snapshot and publish the delta in our changelog.
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