UCMR 5 Sampling Is Finished. Go Look Up Your Building.

Fair warning before you read another word: I sell bottleless water systems for a living. I have a stake in you caring about this. So I'm only going to point you at government data you can check yourself.

Here's the situation. The EPA's Fifth Unregulated Contaminant Monitoring Rule required public water systems to sample for 29 PFAS compounds and lithium during 2023 through 2025. That sampling window is closed. It produced one of the broadest national pictures of PFAS occurrence in drinking water we've had.

And the results are public. EPA publishes the occurrence data and updates it periodically, broken out by individual public water system. You can look up the utility that serves your office building. Nobody needs to give you permission.

Almost nobody does this

I talk to a lot of office managers, facilities people, and owners. When PFAS comes up, the response is usually some version of "our water's fine" or "the city would tell us."

That's a guess dressed up as a fact. The data exists. Looking it up is a short task. The gap between "I assume it's fine" and "I looked it up" is the entire distance between an opinion and a decision.

I get why it doesn't happen. Nobody's job description says audit the municipal water data. It's not on fire. It doesn't show up in a budget meeting. So it sits.

What the numbers get measured against

In April 2024, EPA finalized the first national primary drinking water regulation for PFAS. It set 4.0 parts per trillion for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and GenX, plus a Hazard Index approach for certain mixtures, because these chemicals rarely show up alone. Public systems must finish initial monitoring by 2027 and comply by 2029.

Update, September 2026: in May 2026 EPA proposed letting systems request until 2031 to comply and separately proposed rescinding the PFHxS, PFNA, GenX and mixture limits. The 4.0 ppt PFOA and PFOS limits stay as written; final action on both was still pending when I checked. Either way, there's another wave of monitoring and public reporting coming. The UCMR 5 data is already sitting there, and it's the closest thing to a preview you're going to get.

Why this is worth a few minutes of your afternoon

PFAS are called forever chemicals because they break down very slowly. They've turned up in the blood of people and animals around the world, and in consumer products, food, and water supplies.

The health side isn't speculative hand-waving either. CDC and ATSDR report that national biomonitoring finds PFAS in the blood of nearly everyone tested in the United States, and ATSDR's research summary associates higher exposure with increased cholesterol, changes in liver enzymes, lower antibody response to some vaccines, and kidney and testicular cancer (for PFOA).

And it's not a handful of unlucky zip codes. A 2023 USGS study estimated at least 45% of U.S. tap water has one or more PFAS. Madison is on the list, not off it: PFAS were found at the city's Well 15 in 2017, the well was shut down in 2019, and it only went back into service in September 2025 behind a new activated carbon and ion exchange plant.

The honest caveat

Not everything in the water conversation deserves the same alarm level. On microplastics, WHO's review concluded that at currently measured levels they don't appear to pose a health risk, while noting the evidence base is limited and calling for more research and less plastic pollution.

California has moved earlier than most on that front. It adopted a regulatory definition of microplastics in drinking water in June 2020, standardized test methods in 2021–2022, and four years of required testing, work that traces back to Senate Bill 1422 (2018).

I bring that up because I'd rather you trust me on PFAS than have me oversell everything at once. PFAS has enforceable federal limits and a public dataset. Microplastics has a working definition in one state and an open research question. Those are different situations and they deserve different reactions.

What I actually think

The people who will handle the coming compliance deadlines well aren't the ones with the best vendor. They're the ones who read their own numbers early, while there was still time to think instead of react.

The data's already public. That's the part that gets me. This isn't a problem of access. It's a problem of nobody opening the page.