Drinking water guide
PFAS Contamination by State, EPA UCMR5 Data Analysis
Which states have the most PFAS detections in drinking water, where contamination concentrates and why, and how to find results for your area using PlainWater's data.
Key Takeaway
EPA's UCMR5 program tested 143,000+ water systems for 29 PFAS compounds, generating 1.93 million test results, the most comprehensive national PFAS drinking water survey ever conducted. PFAS were detected in water systems in all 50 states, but concentrations are highest near military bases using AFFF firefighting foam, industrial PFAS manufacturing sites, and agricultural areas where PFAS-laden biosolids were applied. EPA's 2024 final rule sets 4 ppt limits for PFOA and PFOS; water systems must comply by 2029.
The Scale of UCMR5, What the Data Shows
The Fifth Unregulated Contaminant Monitoring Rule (UCMR5) ran from 2023 to 2025 and required approximately 6,900 large water systems (serving 10,000+ people) and a representative sample of smaller systems to test for 29 PFAS compounds. The program generated roughly 1.93 million individual test results, a dataset unprecedented in scope for PFAS monitoring in US drinking water.
The headline finding: PFAS are detectable in water systems across every state. The compound detected most frequently nationally is PFBS (perfluorobutane sulfonic acid), a short-chain PFAS increasingly used as a replacement for PFOS. PFOA and PFOS, the two compounds subject to the strictest new limits, were detected in a significant share of tested systems, with elevated concentrations concentrated in areas near historical contamination sources.
Explore UCMR5 data for any state through PlainWater's state directory or look up individual contaminants through the contaminants directory.
Why PFAS Concentrations Vary by Region
PFAS contamination is not randomly distributed. The geography of contamination follows the geography of PFAS use and disposal. Three primary factors explain most of the geographic variation:
Military installations and AFFF use. Aqueous film-forming foam (AFFF) used in aircraft crash firefighting and training contained PFOS and PFOA for decades. Major bases, including Pease Air Force Base (New Hampshire), Wurtsmith Air Force Base (Michigan), Peterson Space Force Base (Colorado), and Whidbey Island Naval Air Station (Washington) - contaminated surrounding groundwater that feeds nearby water systems. The Department of Defense has identified over 700 installations with known or suspected PFAS contamination from AFFF use.
Industrial PFAS manufacturing and use sites. Regions with PFAS manufacturing history show elevated contamination in a radius around production facilities. 3M's former PFOS manufacturing in Minnesota (Cottage Grove), DuPont and Chemours's PFOA manufacturing in West Virginia (Washington Works), and Chemours's GenX production in North Carolina (Fayetteville Works) are among the most studied examples. Downstream communities drawing surface water from contaminated rivers experienced decades of exposure before the contamination was fully characterized.
Agricultural biosolids application. Treated sewage sludge (biosolids) containing concentrated PFAS has been applied to farmland for decades. In states with intensive agriculture, particularly in the Northeast and Midwest, this pathway has contaminated private wells and small community water systems drawing from shallow groundwater. Maine discovered this problem severely; the state now has restrictions on biosolids application that other states are beginning to adopt.
States with Notable PFAS Detections
The table below summarizes states with elevated PFAS detection rates based on UCMR5 data and prior state-level monitoring programs. "High" detection reflects both detection frequency and concentration levels above health advisory thresholds. All states had some detections, this table highlights where concentrations are most elevated.
| State | Systems Tested | Detection Level | Key Context |
|---|---|---|---|
| Michigan | 1,400+ | High | Major industrial PFAS manufacturing sites; extensive monitoring |
| New Jersey | 600+ | High | Industrial corridor; own state MCLs predating federal rule |
| North Carolina | 700+ | High | Chemours Fayetteville plant (GenX/HFPO-DA) contamination |
| California | 2,800+ | Moderate-High | Multiple military bases; agriculture; state action levels set |
| Pennsylvania | 800+ | Moderate-High | Military and industrial sources in southeast region |
| Ohio | 900+ | Moderate | Industrial midwest; some elevated groundwater near facilities |
| Minnesota | 700+ | Moderate | Twin Cities East Metro 3M contamination; established programs |
| Colorado | 500+ | Moderate | Military base AFFF contamination in Front Range communities |
| Washington | 500+ | Moderate | Joint Base Lewis-McChord and Whidbey Island contamination |
| Texas | 2,000+ | Variable | Large state; some military and industrial sites elevated |
Source: EPA UCMR5 data (2023–2025) and state monitoring programs. Detection levels are relative assessments, not official EPA classifications. Browse full state data at plainwaterdata.com/states/.
Compiled by the PlainWater research team.
The EPA's 2024 PFAS Drinking Water Rule
In April 2024, the EPA finalized the first-ever National Primary Drinking Water Regulation specifically for PFAS, a landmark regulatory action decades in the making. The rule establishes:
- MCL of 4 ppt for PFOA (perfluorooctanoic acid) - near the practical detection limit
- MCL of 4 ppt for PFOS (perfluorooctane sulfonic acid)
- MCL of 10 ppt for PFNA, PFHxS, and HFPO-DA (GenX) individually
- Hazard Index ≤ 1 for any combination of PFNA, PFHxS, HFPO-DA, and PFBS
Water systems have until 2027 to complete initial monitoring and until 2029 to comply with the new limits (EPA proposed extending the PFOA/PFOS deadline to 2031 in May 2026 for systems that apply; not yet final). Systems that exceed the MCLs will need to install treatment, primarily granular activated carbon (GAC), nanofiltration, or reverse osmosis, or seek new water sources. EPA estimates the rule will cost approximately $1.5 billion per year nationally to implement.
Check your contaminant profiles on PlainWater to see detection frequencies and concentration distributions for individual PFAS compounds across the UCMR5 dataset.
Health Effects of PFAS Exposure
PFAS research has accelerated significantly in the past decade. The National Academies of Sciences 2022 report on PFAS exposure and health effects summarized the evidence as follows:
- Sufficient evidence of association: Elevated total cholesterol, decreased antibody response to vaccines, increased risk of kidney cancer (PFOA specifically)
- Adequate evidence of association: Changes in liver enzymes, decreased birth weight, pregnancy-induced hypertension, testicular cancer (PFOA/PFOS)
- Limited/suggestive evidence: Thyroid disease, reproductive effects, type 2 diabetes, breast cancer
Children and pregnant women are considered most vulnerable. PFAS pass through the placenta and accumulate in breast milk. Infants are exposed both prenatally and during breastfeeding. The developmental and immune effects are a particular concern because critical windows of development cannot be recaptured.
These findings directly informed EPA's decision to set the 4 ppt MCL, a level that acknowledges health risks begin at very low concentrations for sensitive populations, not just at the higher levels that older health advisories suggested.
How to Find PFAS Data for Your Area
PlainWater makes UCMR5 PFAS data searchable at multiple geographic levels:
- By state - see state-level PFAS detection rates, number of systems affected, and top contaminants
- By county - compare counties within a state for PFAS prevalence
- By water system - look up your specific utility to see every PFAS compound tested and the detected concentration
- By contaminant - see where a specific PFAS compound is most prevalent nationally
Start with your water system's page for the most actionable information. If PFAS were detected in your system, the page will show which compounds were found and at what levels, allowing you to compare against EPA's 4 ppt MCL for PFOA and PFOS and the health advisory levels for other compounds.
Frequently Asked Questions
Which states have the highest PFAS contamination in drinking water?
UCMR5 data shows states with significant industrial PFAS manufacturing history, large military installations, or extensive AFFF use tend to have the most detections. Michigan, New Jersey, North Carolina, and California appear prominently in national PFAS detection datasets due to their industrial and military footprint. However, PFAS contamination is genuinely nationwide, the UCMR5 program found detectable PFAS in water systems across all 50 states. Detection rates vary significantly by water source type, with groundwater systems showing higher concentrations in some contaminated regions.
What PFAS detection level should concern me?
EPA's 2024 final rule set Maximum Contaminant Levels (MCLs) of 4 parts per trillion (ppt) for PFOA and PFOS, near the practical detection limit for most labs. EPA health advisories for PFNA, PFHxS, and HFPO-DA (GenX) are set even lower, with lifetime health advisory levels below 10 ppt. For the purpose of personal health decisions, any detection above 4 ppt for PFOA or PFOS is worth discussing with your healthcare provider, especially if you are pregnant or have young children. For PFAS with no established MCL, use the health advisory as a reference point.
Why do rural areas sometimes have higher PFAS than urban areas?
Several factors contribute. Rural groundwater systems may draw from aquifers contaminated by nearby agricultural land where PFAS-containing biosolids were applied as fertilizer, or from proximity to military training ranges. Rural systems typically have less treatment infrastructure than large urban utilities. Additionally, rural areas near industrial PFAS manufacturing sites, which historically weren't always located near population centers, may have highly elevated groundwater concentrations. Urban systems often have better treatment capacity and may blend water from multiple sources, diluting contamination.
Do water treatment plants remove PFAS?
Conventional water treatment, coagulation, sedimentation, filtration, chlorination, does not effectively remove PFAS. The treatments that do work are granular activated carbon (GAC) filtration, high-pressure membrane processes (nanofiltration and reverse osmosis), and advanced oxidation. These are significantly more expensive than conventional treatment. Many water systems are in the process of planning or installing PFAS treatment capacity ahead of the 2029 compliance deadline. You can inquire with your utility about their treatment plans if PFAS has been detected in your system.
How does UCMR5 testing differ from routine EPA monitoring?
Routine EPA monitoring covers regulated contaminants with established MCLs, substances for which a legal limit exists. UCMR (Unregulated Contaminant Monitoring Rule) covers contaminants that may present health risks but do not yet have a federal drinking water standard. UCMR5 specifically targeted PFAS and lithium precisely because they were unregulated at the time, and the data collected informs whether a regulation should be set. UCMR5 is a one-time screening; ongoing PFAS monitoring will shift to the routine regulatory framework once the 2024 MCL rule takes full effect.
Will PFAS contamination get worse over time?
The contamination in the environment is unlikely to diminish quickly, PFAS are extremely persistent. However, the major industrial and military discharges that created most contamination have been significantly reduced since the early 2000s phase-outs of PFOA and PFOS. Ongoing sources include biosolids application, legacy landfills, and some continued industrial use of short-chain PFAS replacements. Water utilities are investing heavily in treatment capacity. The longer-term picture depends on regulatory enforcement, remediation of known source sites, and whether new PFAS compounds emerge from ongoing industrial use.
Sources
- U.S. EPA, UCMR5 Contaminant Data (epa.gov/dwucmr): 1.93M PFAS results, 2023–2025
- U.S. EPA, PFAS National Primary Drinking Water Regulation (April 2024, 89 FR 32532)
- National Academies of Sciences, Engineering, and Medicine, Guidance on PFAS Exposure, Testing, and Clinical Follow-Up (2022)
- U.S. Department of Defense, PFAS in the Environment (defense.gov/PFAS)
- Environmental Working Group, PFAS Contamination in the U.S. (ewg.org)
- PlainWater database, 143K water systems, 1.93M PFAS results, 157 contaminants (EPA SDWIS + UCMR5)
This content is for informational purposes only. PFAS science and regulation are rapidly evolving. For the most current data and guidance, consult your state drinking water program or the EPA PFAS website. If you have health concerns related to PFAS exposure, consult your healthcare provider.