UCMR 5 explained, how to read your utility's PFAS data

What UCMR 5 actually is

The Unregulated Contaminant Monitoring Rule (UCMR) is the mechanism the US Environmental Protection Agency uses to collect occurrence data on drinking-water contaminants that are not yet subject to a National Primary Drinking Water Regulation (NPDWR). It is authorised by the Safe Drinking Water Act and codified at 40 CFR §141.40. Every five years, EPA selects up to 30 contaminants to monitor across a representative sample of US public water systems. The fifth cycle, UCMR 5, was finalised on 27 December 2022 (87 FR 80415) and is the most consequential round to date because of one thing: it is dominated by PFAS.

UCMR 5 requires sampling for 29 individual per- and polyfluoroalkyl substances (PFAS) plus lithium. Unlike earlier cycles, which sampled only a statistically selected slice of large utilities, UCMR 5 captures every public water system (PWS) serving 3,300 people or more, plus a nationally representative sample of smaller systems serving 25–3,299 people. EPA estimates roughly 6,000 utilities are covered in the larger tier, producing the broadest PFAS-occurrence dataset ever assembled for US drinking water. If your tap is on a community water system in a town larger than a few thousand people, your utility is in UCMR 5.

The practical consequence: for the first time, an ordinary household can look up their own utility and see real PFAS measurements rather than relying on advocacy-group estimates or geographic models. That is what this guide walks through.

Timeline

UCMR 5 sampling runs over a three-year window, but each individual utility samples for a much shorter slice of it. The rule assigns every PWS to a 12-month sampling year, calendar 2023, 2024, or 2025, and requires four quarterly samples within that year for surface-water systems (twice-yearly for groundwater systems, taken 5–7 months apart). Results are submitted to EPA by the certified laboratory that ran the analysis, not by the utility, which removes one common source of paperwork drift.

EPA publishes the rolling results to NCOD on a quarterly cadence. Early data from 2023 sampling years went public starting in August 2023; the final dataset will be complete sometime in 2026 after the last 2025 samples are validated. If you look up your utility today and see no rows, the most likely explanation is that the system is scheduled for a later sampling year, not that the system tested clean.

The 29 PFAS analytes, what's covered and what isn't

UCMR 5 uses two EPA analytical methods to cover the 29 PFAS: Method 537.1 (Version 2.0) handles 18 of the compounds, and Method 533 handles 25 (with overlap on several short-chain compounds). Together they capture the headline regulated four, PFOA, PFOS, PFHxS, PFNA, plus HFPO-DA (the "GenX chemicals"), PFBS, and a long tail of short-chain replacements and precursors. Each compound has its own minimum reporting level (MRL) set by EPA, calibrated to what the methods can reliably quantify in finished drinking water.

Below is a working subset of the analyte list with EPA's published MRLs. Full MRLs for all 29 are in the UCMR 5 final rule and the analytical method documents.

What is not in UCMR 5 matters too. The methods quantify discrete, named PFAS, they do not return a total-organic-fluorine number, and they do not detect ultra-short-chain compounds like trifluoroacetic acid (TFA) or PFPrA. They also do not detect most large polymeric or precursor PFAS that may transform into regulated compounds in the environment. If your utility's UCMR 5 row reads "ND" for every analyte, that means none of the 29 named compounds exceeded their MRL, not that the water is "PFAS-free" in an absolute sense. For background on why specific compounds matter most for human health, see our PFOA and PFOS toxicology summary.

How to look up your utility on NCOD

EPA hosts the National Contaminant Occurrence Database at ncod.epa.gov. It is the only official source for UCMR data. Third-party dashboards (EWG, state portals, news projects) re-package the same underlying NCOD extracts, sometimes with lag and sometimes with their own filtering, for a definitive answer always go to NCOD itself.

The lookup, step by step:

1. Find your PWSID (Public Water System Identification number). It is a nine-character code beginning with your state's two-letter postal code (e.g. CA1910067 for the Los Angeles Department of Water & Power). Your annual Consumer Confidence Report (CCR), often called a "water quality report", lists it on the first or last page. If you can't find the CCR, search "[your utility name] PWSID" or use EPA's Safe Drinking Water Information System (SDWIS) Federal Reporting Services.
2. Go to ncod.epa.gov and choose the UCMR 5 occurrence dataset.
3. Filter by PWSID (most precise) or by state and system name.
4. Download the result rows as CSV. Each row represents one analyte at one sampling event at one sampling point within the system.

NCOD also publishes the full national UCMR 5 dataset as a single bulk CSV that can be downloaded and queried offline, this is what most researchers and journalists actually work with. If you would rather skip the spreadsheet step, our $15 PFAS brief pulls and interprets the rows for your utility automatically.

How to read the result row

A UCMR 5 result row contains a handful of fields that all matter. The key ones:

• Contaminant, the named PFAS analyte (e.g. PFOA).
• AnalyticalResultsSign, either = (a detection at the listed value) or < (a non-detect, where the value shown is the MRL, not the actual concentration).
• AnalyticalResultValue, the numerical result in µg/L in the raw NCOD download. Most published summaries convert this to ng/L (nanograms per litre, equivalent to parts per trillion, ppt) by multiplying by 1,000. 0.004 µg/L = 4 ng/L = 4 ppt.
• SamplePointName / SamplePointType, distinguishes entry-point-to-distribution-system (EPTDS) samples from raw or distribution-system samples. The MCL-relevant samples are EPTDS.
• CollectionDate, when the sample was taken.

Two distinctions trip people up. First, a row tagged with < means the lab did not detect the compound above its MRL, it does not mean the result was zero. The compound may be present at a level below the MRL (which for several PFAS is 3–5 ng/L), in which case the row reads as a "non-detect" even though there is technically PFAS in the water. Second, "non-detect" and "below MRL" are sometimes used interchangeably, but strictly speaking the MRL is the lowest concentration the method can reliably quantify; some labs also report a lower "method detection limit" (MDL) below which a compound may still be qualitatively detectable but not quantifiable.

Comparing your result against the April 2024 MCLs

On 10 April 2024, EPA finalised the first-ever National Primary Drinking Water Regulation for PFAS, setting enforceable Maximum Contaminant Levels (MCLs) for six PFAS. These MCLs are now codified at 40 CFR §141.61(c). The relevant numbers for reading your UCMR 5 row:

Note that for PFOA and PFOS the MRL equals the MCL. That means UCMR 5 cannot distinguish "non-detect" from "right at the MCL" for those two compounds, any "below MRL" row could still be at 0–3.99 ng/L, which is below the new enforceable level but not necessarily a clean result by stricter state benchmarks. Several states (Michigan, New York, New Jersey, Massachusetts) have set their own MCLs that are at or below the UCMR 5 MRL for at least one PFAS. See our state PFAS regs comparison for the full picture, and our explainer on the April 2024 MCL package for the regulatory back-story.

The Hazard Index MCL is the only one that requires you to do arithmetic. Take the measured value of each of PFHxS, PFNA, HFPO-DA, and PFBS in ng/L, divide each by its individual Health-Based Water Concentration (10, 10, 10, and 2,000 ng/L respectively), and sum the four ratios. A total above 1.0 exceeds the MCL.

Limitations of UCMR 5 data

UCMR 5 is a transformative dataset, but it has real limits, pretending otherwise is how the data gets misread.

It is a snapshot, not continuous monitoring. A surface-water system gets four samples in twelve months; a groundwater system gets two. PFAS concentrations vary with source-water mixing, treatment changes, seasonal rainfall, and discharge events at upstream industrial sites. A row that reads 3.8 ng/L PFOA in one quarter could read 8.1 ng/L the next without anything visibly different at the utility. Once the new NPDWR's compliance monitoring begins in 2027, sampling becomes more frequent and ongoing, but UCMR 5 itself is a one-year snapshot per system.

Smaller systems are under-represented. The 25–3,299-person tier is sampled only as a nationally representative random subset (roughly 800 systems), not every small system. Rural community water systems are therefore less likely to have UCMR 5 data for their own PWSID specifically; many will need to wait for the post-NPDWR compliance monitoring cycle or commission their own testing.

Private wells are not covered at all. If your tap is on a private well, you have no UCMR row, full stop. EPA's PFAS regulations apply to public water systems, not individual wells. For private-well PFAS exposure context, see our PFAS groundwater hotspot map.

The MRL ceiling caps what can be inferred. Because PFOA and PFOS MRLs sit at the MCL value, UCMR 5 cannot quantify low-level PFOA/PFOS exposure below 4 ng/L, even though human health-effect studies (ATSDR Toxicological Profile for Perfluoroalkyls, 2021) discuss exposures well below that threshold. UCMR 5 is fit for the regulatory question ("does this utility exceed the new MCL?") but not for the toxicological question ("what is my total PFAS body burden?").

It does not account for in-home contributions. Premise plumbing (fittings, fluoropolymer-lined pipes, water-using appliances) and point-of-use treatment are outside UCMR 5's scope. Your kitchen-tap concentration may differ from the entry-point sample EPA published. For the filter-selection side of that question, our guide on NSF 53 P473 vs NSF 58 PFAS filters walks through the certifications worth looking for.

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