PFAS in Your Drinking Water: How to Check Your City's Contamination Level

For years, PFAS contamination in public drinking water was poorly documented and even more poorly disclosed. That changed with the EPA's UCMR 5 monitoring program, which collected the most thorough PFAS data ever assembled from U.S. water systems. The results are sobering. Here's how to find out what was in your tap water, and what to do with that information.

What UCMR 5 Is and Why It Matters

UCMR 5 is the fifth iteration of the EPA's Unregulated Contaminant Monitoring Rule. Every five years, the EPA requires public water systems above a certain size to test for contaminants that aren't yet regulated but are suspected health risks. The results go into a national database that the EPA and researchers use to evaluate whether new regulations are warranted.

UCMR 5, which covered 2023 to 2025, was the first mandatory federal monitoring specifically targeting PFAS compounds. Previous UCMR rounds had limited PFAS coverage; UCMR 5 required testing for 29 PFAS compounds, including PFOA, PFOS, PFNA, PFBS, PFHxS, and PFDA — the compounds with the most established health research.

Coverage: All public water systems serving 3,300 or more people were required to test. The EPA also conducted voluntary sampling of smaller systems. In total, the UCMR 5 data covers systems serving approximately 220 million Americans.

Results released: The first UCMR 5 data became public in mid-2024. It confirmed what environmental researchers had suspected: PFAS contamination in public water supplies is widespread, affecting systems across most states, with the highest concentrations typically near military bases, airports, industrial facilities, and certain municipal water sources downstream from manufacturing plants.

How to Check Your Water System

There are three reliable ways to check your specific exposure:

1. EPA's UCMR 5 Data Dashboard

The EPA maintains a searchable database of UCMR 5 results at epa.gov. Navigate to the "Drinking Water" section and look for the UCMR 5 data portal. You can search by water system name, state, or PWSID (Public Water System ID, a unique identifier assigned to each water utility).

If you don't know your water system's name, look at your water bill or call your local utility. The Consumer Confidence Report that utilities are required to mail annually also lists the system's PWSID.

2. EWG's Tap Water Database

The Environmental Working Group maintains a more user-friendly interactive database at ewg.org/tapwater. Enter your zip code to see PFAS and other contaminant results for your water system, along with EWG's own health guidelines (which are typically stricter than EPA limits). EWG's database incorporates UCMR data as well as state-level testing results.

3. Your Annual Consumer Confidence Report

Every public water utility in the U.S. is required to send customers an annual Consumer Confidence Report (CCR) by July 1 of each year, disclosing detected contaminants and their levels. As PFAS MCLs went into effect, utilities became required to include PFAS data in their CCRs. If you haven't received one, call your utility and ask.

Well water users: UCMR 5 data covers public water systems, not private wells. If you get water from a private well, the only way to know your PFAS levels is to test. Look for a certified laboratory in your state through the EPA's certified laboratory list or your state environmental agency's website. A thorough PFAS panel typically costs $150 to $400.

Understanding the 4 ppt MCL

On April 10, 2024, the EPA finalized the first federal maximum contaminant levels (MCLs) for PFAS in drinking water. The rule set:

• PFOA: 4 parts per trillion (ppt)
• PFOS: 4 ppt
• PFNA: 10 ppt
• PFHxS: 10 ppt
• PFDA: 10 ppt
• HFPO-DA (GenX): 10 ppt
• Mixed PFAS (hazard index): Combinations of PFNA, PFHxS, PFDA, and HFPO-DA must meet a combined hazard index of 1

For scale: 4 ppt means 4 parts per trillion, equivalent to 4 drops of water in an Olympic-size swimming pool. These are extremely small concentrations, which speaks to how biologically potent PFAS compounds are at low doses — they accumulate in body tissue over time.

The 4 ppt limit for PFOA and PFOS was controversial. Industry groups challenged it in court, arguing the limits were set below what science could reliably measure. Public health advocates argued the science supports a limit of zero, given that PFAS are carcinogens with no safe threshold.

Water systems have until 2027 to comply with the new MCLs. During the compliance period, many utilities will be required to install treatment infrastructure — typically granular activated carbon (GAC) or reverse osmosis (RO) filtration — to bring PFAS levels down.

What Your Numbers Mean

When you look up your water system's UCMR 5 data, you'll see results expressed in ppt (parts per trillion) or ng/L (nanograms per liter, which is equivalent).

Below 4 ppt PFOA and PFOS: Below the federal MCL. Your water is compliant with current EPA rules. This doesn't necessarily mean zero risk — it means the detected level is below the threshold the EPA determined was the limit of enforceable regulatory feasibility.

4 ppt to 20 ppt: This range is where regulatory debate is most active. Your water is above the federal MCL for PFOA/PFOS but below levels that historically triggered public health actions before 2024.

Above 20 ppt: Significantly elevated. This level triggers more immediate regulatory response and may indicate proximity to a significant PFAS source (manufacturing, military installation, or industrial facility).

Above 70 ppt: The pre-2024 EPA health advisory level. Water systems with historical data showing levels in this range were subject to older guidance that was widely criticized as inadequate. Many of these systems have been identified in AFFF-related or industrial PFAS contamination cases.

For context on how PFAS contamination connects to health conditions and legal claims, see our full drinking water contamination guide and our page on PFAS health effects.

Health Risks of Long-Term PFAS Exposure

PFAS compounds have been studied for their health effects since the 1990s, when 3M's own internal research documented accumulation in the blood of workers and consumers. The research base is now extensive.

The strongest epidemiological evidence links PFAS exposure to:

• Kidney cancer — RCC (renal cell carcinoma) has been the most consistently documented cancer outcome in high-exposure populations
• Testicular cancer — Multiple occupational cohort studies have found elevated rates in PFAS-exposed workers
• Thyroid disease — Disrupted thyroid hormone levels documented in both occupational and community exposure studies
• High cholesterol — Consistently elevated LDL cholesterol in high-exposure cohorts
• Immune system suppression — Reduced vaccine efficacy and immune response documented in children and adults
• Reproductive effects — Reduced fertility, pregnancy complications, low birth weight
• Bladder cancer — Emerging association in multiple datasets

The disease does not announce itself as "PFAS-related." People who lived for years near contaminated water sources may develop cancer without ever connecting it to what came out of their tap. That's partly what the UCMR 5 data is designed to change.

Legal Options If Your Water Was Contaminated

Documentation of PFAS contamination in your water supply is a starting point for legal analysis, not an automatic ticket to compensation. The legal picture is complicated, with different tracks depending on your situation:

Municipal claims (already settled): 3M's $10.3 billion settlement and DuPont's separate settlement package specifically cover municipal water utilities seeking to fund treatment infrastructure. These settlements don't include individual personal injury claims. For more on this, see our full breakdown of the 3M settlement and what it means for individuals.

Individual personal injury claims: If you lived in a contaminated water area and developed cancer or another PFAS-related health condition, personal injury litigation may be available. These cases are separate from the municipal settlements and require establishing your exposure history, your diagnosis, and the link between them.

AFFF-related claims: If you or a family member served at a military installation or was a civilian firefighter exposed to AFFF foam, there's a separate litigation track. See our AFFF cancer litigation overview.

Related Resources

• PFAS in Drinking Water: Full Guide
• What Are PFAS "Forever Chemicals"?
• PFAS Health Effects: Cancer and Other Conditions
• The 3M Settlement and What It Means for You
• AFFF and Military PFAS Cancer Claims

Frequently Asked Questions