How PFAS Estimator works

1. 1

   Match the system name

   A ZIP code can contain several water systems. Find the utility name on your water bill and use the result for that system. The ZIP search alone cannot identify the supplier for a specific address.

2. 2

   Check the yearly averages

   The site shows the highest yearly average across each system’s EPA sampling locations. It is not a measurement from your kitchen faucet.

3. 3

   Use the comparison as a next-step signal

   “At or above” means at least one complete EPA result reached the comparison used in this release. It does not mean every home has the same level or that this website has made a compliance decision.

The research paper asks a separate national question: whether PFAS results across community water systems vary with the racial, ethnic, economic, and rural composition of their service areas after accounting for system size, water source, ownership, and region. That analysis is ecological and cross-sectional; it does not assign exposure or health outcomes to individuals.

• PFAS monitoring: EPA UCMR 5 occurrence records received through January 15, 2026 and EPA’s January 2026 Average PFAS Results export.
• System characteristics: EPA SDWIS Federal Reporting Services.
• Service areas: EPA Public Water System Service Areas version 3, including system-sourced and modeled boundaries.
• Demographics: 2020–2024 American Community Survey block-group estimates and Census Planning Database urban/rural fields.
• ZIP lookup only: EPA’s PWS-reported UCMR service-ZIP associations.

EPA described the January 2026 data as approximately 95% of expected UCMR 5 results and planned a final release for fall 2026. The manuscript must identify this as an interim federal release and perform one controlled refresh before submission if the final release is available.

UCMR 5 attempted to monitor all eligible systems serving at least 3,300 people and selected 800 smaller systems through a population-weighted, source- and size-stratified design intended to support national occurrence estimates. Public row-level inclusion probabilities or analysis weights were not identified. The primary inferential cohort therefore includes active community water systems serving at least 3,300 people with complete monitoring, an eligible service-area boundary, and sufficient demographic coverage.

The 632 monitored smaller community systems with eligible demographic records are reported separately as an explicitly unweighted sensitivity; they do not represent all small U.S. systems. Nontransient noncommunity systems are excluded from demographic models because residential Census characteristics do not describe school, workplace, hospital, and other nonresidential populations.

1. 1

   Use complete sampling sets

   Annual averages are defined at an EPA sampling location using its complete required monitoring set. Results below the UCMR minimum reporting level are assigned zero for the calculation.

2. 2

   Reproduce EPA classifications

   The primary source is EPA’s January 2026 Average PFAS Results export. A record-level reconstruction is retained as a validation analysis rather than as a substitute for unresolved replacement-record logic.

3. 3

   Classify the combined primary outcome

   A system is positive when at least one complete-set location meets an April 2024 individual-compound or qualifying-mixture technical comparison.

These cutoffs reconstruct a rounded federal comparison; they are not newly proposed toxicological thresholds. The manuscript and website use “benchmark” or “technical comparison,” never “violation” or “noncompliance.” Compound-specific outcomes are secondary. Sparse or nonconvergent adjusted models are reported descriptively rather than forced into unstable estimates.

EPA’s water-system-to-2020-Census-block-group crosswalk links each system service area with block groups. The primary aggregation uses residential-building-footprint weights; area weighting is a sensitivity. Demographic records are retained when block-group links with valid core measures cover at least 90% of the crosswalk-estimated population.

The joint model includes service-area percentages Hispanic/Latino, non-Hispanic Black, non-Hispanic American Indian/Alaska Native, below the federal poverty level, and rural. System covariates are log₂ population served, source-water category, ownership, and EPA region.

Connecticut’s planning-region transition changed block-group identifiers in current Census products. For Connecticut only, the analysis uses the official 2023 Planning Database to recover geography-aligned 2017–2021 ACS characteristics and 2020 urban/rural counts on the original 2020 identifiers used by EPA. All 56 primary-cohort systems using that fallback are flagged; a latest-vintage-only sensitivity excludes them.

• Adjusted prevalence ratios are estimated with modified Poisson regression.
• EPA-region fixed effects address broad regional differences; leave-one-region-out analyses assess influence.
• Residual spatial autocorrelation is tested using permutation-based Moran’s I at 4, 8, and 12 nearest neighbors.
• Because the prespecified diagnostic remained positive, primary uncertainty uses a Conley-style spatial heteroskedasticity-and-autocorrelation-consistent sandwich estimator with a 250-km Bartlett kernel.
• State-clustered variance and 100- and 500-km spatial cutoffs are uncertainty sensitivities.
• Secondary compound-specific coefficients are subjected to event-count and convergence gates and Benjamini–Hochberg false-discovery-rate control.

The spatial amendment was logged after the residual diagnostic rather than presented as prespecified. At eight neighbors, the primary-model Pearson residual Moran’s I was 0.119 (999-permutation two-sided P=.001).

Required sensitivity analyses include area versus building weights, latest-vintage Census data only, all monitored CWSs as an unweighted sample, system-sourced service boundaries only, alternative spatial cutoffs, leave-one-EPA-region-out refits, and size/source strata. A model is not reported when separation or nonconvergence makes the estimate unreliable.

Of 8,069 primary-cohort systems, 964 (11.9%) met at least one April 2024 technical comparison. In the joint adjusted model, each 10-percentage-point higher Hispanic service-area composition corresponded to a prevalence ratio of 1.15 (95% CI, 1.09–1.22). Estimates for non-Hispanic Black composition (PR, 1.02; 95% CI, 0.93–1.11) and non-Hispanic American Indian/Alaska Native composition (PR, 1.18; 95% CI, 0.91–1.53) were null or imprecise.

Poverty composition (PR, 0.74; 95% CI, 0.64–0.87) and rural composition (PR, 0.94; 95% CI, 0.91–0.97) were inversely associated with the combined benchmark outcome. These directions must be reported as prominently as the positive Hispanic-composition association and investigated—not rationalized away.

The Hispanic-composition estimate was similar across the primary geographic, cohort, uncertainty, regional-influence, and most size/source sensitivities. Stability does not convert an ecological cross-sectional association into a causal or individual-level claim.

The ZIP lookup reads directly from the frozen scientific export. It finds water systems connected with the entered ZIP and displays their EPA yearly averages. The website does not recalculate the paper’s results, fill in missing values, or create a health-risk score.

The PFAS Health Assistant is optional. It receives a short text summary of the water systems shown only after a visitor asks a question. It can explain terms, health research, utility follow-up, and filter guidance, but it cannot change a number or comparison on the page. If the assistant is unavailable, the ZIP lookup continues to work.

EPA: Reducing PFAS in Your Drinking Water with a Home Filter →

• Ecological design: service-area composition cannot be assigned to individuals and cannot establish individual exposure.
• Cross-sectional timing: associations do not establish causality or historical exposure.
• Interim release: the January 2026 UCMR 5 file is not the final federal release.
• Service-area uncertainty: some EPA boundaries are modeled, and demographic interpolation does not eliminate within-area heterogeneity.
• Small-system sampling: unweighted monitored systems below 3,300 people do not support inference to all small systems or demographic subgroups.
• Correlated community measures: compositional predictors are interdependent; adjusted coefficients are not isolated causal effects.
• Benchmark interpretation: technical-assistance classifications based on UCMR monitoring are not regulatory compliance determinations.
• Population totals: summed reported system populations can double-count people served through wholesale-retail networks.
• Policy instability: the federal regulatory configuration may change after this release.

Automated tests cover annual-average comparison rules, Hazard Index classification, prevalence-ratio recovery, and false-discovery-rate behavior. The EPA average-results normalization was validated against the January 2026 federal summary counts. Release artifacts carry cryptographic hashes.

The manuscript and analysis have not completed independent peer review. Planned or requested review is not represented as completed review, institutional endorsement, or authorship. Authorship must reflect substantive contribution, accountability, final approval, and the ability to defend the work; family relationship, title, or affiliation is not evidence of contribution.

The remaining high-priority external review targets are below-quantitation handling, mixture construction, service-area interpolation, compositional modeling, spatial inference, and the final policy interpretation. Any resulting method change must be logged and rerun through the same pipeline.

1. US Environmental Protection Agency. Fifth Unregulated Contaminant Monitoring Rule Data Finder.
2. US Environmental Protection Agency. Selection of Nationally Representative Public Water Systems for UCMR: 2021 Update. EPA 815-B-21-012.
3. US Environmental Protection Agency. PFAS drinking-water rule implementation.
4. US Environmental Protection Agency. Proposed PFAS rescission rule.
5. US Environmental Protection Agency. Public Water System Service Areas.
6. US Environmental Protection Agency. Reducing PFAS in Your Drinking Water with a Home Filter.
7. NSF. PFAS in Drinking Water: Filter Certification Guidance.
8. US Census Bureau. American Community Survey 5-year data.
9. Conley TG. GMM estimation with cross sectional dependence. Journal of Econometrics. 1999;92(1):1–45. doi:10.1016/S0304-4076(98)00084-0.