The Final U.S. PFAS Water Dataset Is Now Public

In August 2026, the Environmental Protection Agency closed a three-year national sampling effort and published the final dataset from its fifth Unregulated Contaminant Monitoring Rule, known as UCMR 5. The scale is unusual: roughly 10,300 public water systems generated results for 29 per- and polyfluoroalkyl substances, or PFAS, plus lithium.

For the public, the most important feature may be access. EPA's online finder can be filtered by water-system name, state, source-water type, contaminant and result. A national technical program has become locally searchable.

That transparency is valuable. It also creates an easy opening for results to be read too quickly.

What UCMR 5 Was Built to Do

The Safe Drinking Water Act directs EPA to collect national occurrence data for selected contaminants that are not subject to a federal standard when a monitoring rule is established. Some PFAS became regulated while UCMR 5 was underway. The program required monitoring between 2023 and 2025 by every community and non-transient non-community system serving at least 3,300 people, plus a nationally representative sample of 800 smaller systems.

The program asked a basic set of questions: Where are these compounds being measured? At what concentrations? How many people could potentially be served by affected systems? The answers help EPA evaluate future regulatory and technical actions.

This was not a one-time test of every household tap. Systems sampled at designated entry points to the distribution system, not at individual household taps. Groundwater locations generally had two sampling events over 12 months; surface-water locations generally had four. One system can have several sampling locations, and conditions can change after monitoring through treatment, blending, well closures or other operational decisions.

The dataset is therefore a detailed national snapshot, not a permanent verdict on an address.

Detection Starts at a Reporting Limit

Each UCMR result is compared with a minimum reporting level, or MRL. The MRL is the lowest concentration laboratories may consistently report within this federal program. It is based on analytical capability and quality control—not on a boundary between safe and unsafe.

When the finder displays "less than MRL," it means the compound was not reported at or above that program threshold. It does not mean that a laboratory proved the absolute absence of every molecule. Conversely, a result at or above the MRL means the method measured the compound at a reportable concentration. Detection alone does not establish a violation or a health outcome.

Units matter, too. EPA publishes UCMR 5 chemical results in micrograms per liter, equivalent to parts per billion. PFAS regulations are often discussed in nanograms per liter, or parts per trillion. Converting from the former to the latter requires multiplying by 1,000.

A detection is a measurement. Compliance is a legal calculation.

Why These Results Are Not Compliance Results

EPA finalized federal drinking-water limits for several PFAS in 2024. For PFOA and PFOS, the maximum contaminant level is 4.0 parts per trillion. Yet EPA explicitly warns that a UCMR 5 result does not determine whether a system complies with that rule.

Formal compliance is based on a running annual average of quarterly compliance samples from each sampling point, reported to the agency with primary enforcement authority. UCMR 5 used its own monitoring design. For public understanding, EPA calculated location averages where a complete UCMR set was available and compared them with the 2024 limits, but it labels that comparison as technical assistance only.

There is another current wrinkle. On May 18, 2026, EPA proposed keeping the PFOA and PFOS maximum contaminant levels at 4.0 parts per trillion while creating a federal exemption process through which eligible systems could request two additional years—until April 26, 2031—to comply. In a separate proposal, EPA would rescind the individual standards for PFHxS, PFNA and HFPO-DA and the Hazard Index standard for mixtures of those three PFAS plus PFBS. Both comment periods closed July 20, 2026. As of September 2, 2026, both actions remain proposed, so the 2024 rule remains in force.

How to Look Up a Local Result Responsibly

Begin with the exact water-system name on a bill or annual Consumer Confidence Report. In the UCMR 5 finder, check the sample date, location, contaminant, unit and MRL. If a result appears above a comparison value, read the system's current notices and contact the utility for its latest monitoring and response.

An absent listing may simply mean that a small system was not selected for UCMR 5. A listed detection may also describe a historical sample from a location that has since changed. The database is a starting point for a precise conversation, not a substitute for current system information.

It also describes public water systems, not bottled water. Bottled water is regulated separately by the Food and Drug Administration, and product-specific conclusions require product-specific testing.

Better Data Should Produce Better Questions

The final UCMR 5 release does not reduce a complicated national picture to "clean" and "contaminated." Its achievement is more useful: a common set of methods, a broad field of sampling and a public record that can guide treatment, funding and future standards.

The same discipline should shape any water-quality claim. Name the sample. Name the method. State the reporting limit. Separate what was measured from what the law requires. That is how a very large dataset becomes reliable public knowledge rather than a very large headline.

Sources

• EPA: Fifth Unregulated Contaminant Monitoring Rule
• EPA: Final UCMR 5 data summary, July 2026
• EPA: UCMR 5 Data Finder and data considerations
• EPA: Occurrence data from the Unregulated Contaminant Monitoring Rule
• EPA: Final PFAS National Primary Drinking Water Regulation
• EPA: Proposed PFOA and PFOS compliance extension rule
• EPA: Proposed PFAS rescission rule
• FDA: How bottled water is regulated