PFAS in drinking water: reading UCMR 5 results and the Massachusetts limit
What ng/L results mean, the EPA 4.0 ng/L limits for PFOA and PFOS, the Massachusetts 20 ng/L PFAS6 standard, and what to ask a supplier.
A source is not an exposure measurement. Health effects depend on the chemical or physical agent, whether it reaches a person, its concentration, exposure route, duration and individual susceptibility.
Why living near pfas in drinking water may matter
PFAS are persistent chemicals linked in studies to effects on cholesterol, immune response, birth weight and some cancers at sustained exposure. EPA set limits of 4.0 ng/L for PFOA and PFOS in 2024 (compliance deadlines and the limits for three other PFAS are under EPA reconsideration). Massachusetts has enforced 20 ng/L for the sum of six PFAS since 2020.
How it could actually reach a home
Results here are from samples at treatment plants or entry points to the distribution system, not at a tap. A private well is not covered by any of this data and needs its own test.
What a map cannot tell you
- Current levels after any treatment installed since sampling
- Results for small systems and private wells not in the federal survey
- Levels at the tap in this building
What to check next, and who can answer
- Water supplier: Ask for the most recent PFAS results, the treatment in place and the compliance schedule if a limit was exceeded.
- Seller / inspector: For a private well, request PFAS test results or arrange a test with a certified laboratory.
- State drinking-water program: Ask whether the system is under a PFAS order and where the public notices are.
The numbers, in context
- UCMR 5 reporting levels are close to 4 ng/L for PFOA and PFOS, so a "not detected" result means below that level, not zero.
- EPA set 4.0 ng/L limits for PFOA and PFOS in April 2024 and later proposed extending the compliance deadline to 2031; limits for PFHxS, PFNA and HFPO-DA (10 ng/L) and the mixture hazard index are under reconsideration. Check EPA for the current status.
- Massachusetts has enforced 20 ng/L for the sum of six PFAS (PFOS, PFOA, PFHxS, PFNA, PFHpA, PFDA) since 2020, with statewide testing beyond the federal survey.
- A PFAS6 sum shown on NimbyCheck is computed only within a single sample; the highest value across samples is shown, which is an upper bound for that system's sampled water.