EPA's UCMR 5 results for six PFAS (the five with 2024 limits, plus PFBS) and lithium, summarised per US public water system. 10,313 systems, read 2026-10-31. Free to download and reuse with attribution.
datapackage.json — column descriptions, sources and licence (Frictionless Data format)
Licence: our compilation is CC BY 4.0 (attribution: "Do Your Own Math, doyourownmath.com/water/data"). The underlying EPA data is US public domain. Files are versioned by the read date and are not overwritten; a new read gets a new file name and a line in the changelog below.
How to cite
Do Your Own Math (2026). EPA UCMR 5 PFAS and lithium results by US public water system, v1, data read 2026-10-31. https://doyourownmath.com/water/data/ — compiled from US EPA UCMR 5 occurrence data (final dataset, August 2026) and SDWIS.
If you use a single system's figures, cite the system page: it carries the sample window, the read date and the same disclaimer as this page.
What this page is: a plain-language restatement of public test results that the US EPA published for each water system, with the dates of the samples and the date we read them. It describes the system, not the water at your tap, which also depends on the pipes in your building. It is not a safety verdict, not medical advice and not a recommendation to buy anything: "buy nothing" is one of the outcomes in the cost section below. We earn nothing from any link on this page.
Method
What the source is
The Unregulated Contaminant Monitoring Rule 5 (UCMR 5) required every US public water system serving more than 3,300 people, plus a sample of smaller systems, to test for 29 PFAS and lithium between 2023 and 2025. EPA published the results as a final dataset in August 2026. We downloaded that dataset on 2026-10-31 (1,991,977 result rows) and kept the rows for seven substances (464,809 rows): the five PFAS with a 2024 federal limit (PFOA, PFOS, PFHxS, PFNA, HFPO-DA), PFBS as a member of the 2024 hazard index, and lithium as the non-PFAS substance in the programme.
What each number means
Samples: the number of results for that system and substance across all its sampling points and sample events.
Detections ("found"): results EPA reports as a measured value, which means at or above the laboratory minimum reporting level (MRL). "Below the reporting level" means the laboratory did not find the substance above its minimum reporting level (MRL), the smallest amount the EPA method reports. It is a laboratory threshold, not a health threshold, and it is not the same as zero.
Highest: the single highest result at any entry point or tap. It is not an average and not what reaches any particular home.
Units: EPA reports in µg/L; the 2024 rule is written in ng/L. We converted everything to ng/L (1 µg/L = 1,000 ng/L). Pages show lithium in µg/L for readability.
Above the 2024 limit: "yes" when the highest value exceeds the 2024 maximum contaminant level. A single sample above a 2024 limit is a measurement, not a violation. Compliance is judged on running yearly averages, and water systems have until 2029 to meet the limits. On 20 May 2026 EPA proposed giving qualifying systems until 2031 for PFOA and PFOS and removing the limits for PFHxS, PFNA and HFPO-DA; those proposals were not final when we last checked (5 Nov 2026).
Population, source type and connections: from EPA's SDWIS through Envirofacts, for community systems serving more than 25,000 people; smaller systems have no population figure in our files.
ZIP codes: the ZIP finder uses the ZIP list each system reported to EPA for UCMR 5 (20,768 ZIP codes).
What is not in this data
Other substances (lead, nitrate, disinfection by-products, bacteria): see the utility's yearly Consumer Confidence Report.
Compliance records and violations (EPA SDWIS): planned as a separate, separately dated layer.
Anything after the last sample date, and anything about the pipes inside a building.
Totals at this read
10,313 systems; 5,488 with at least one PFAS found above the reporting level; 1,734 with at least one sample above a 2024 limit; 4,825 with none found above the reporting level. Counts are per system, not per person.
How the pages are made
Every sentence on a system page is generated by code from a data field or from a fixed text block (wording policy); no sentence is written by a language model. An automated test refuses any page that lacks the disclaimer, puts the cost section above the results, or contains a word from our banned list ("safe", "unsafe", brand names and the like). Pages with a value above a limit are also checked by hand against a five-item list before publication.
Refresh and corrections
The ingest runs on a schedule (quarterly) and whenever EPA publishes a new release; each read gets a new file version. Corrections are public: what changed. To report an error, use the feedback form (no account or e-mail needed).
Changelog
v1 · 2026-10-31: first public release. UCMR 5 final dataset (August 2026), SDWIS read the same day. 10,313 systems, 72,155 result rows.