How this site works
Methodology
Every local page starts with a public EPA record. When the link between a ZIP code and a utility is uncertain, or the utility's record is too thin, the site says so or shows the county overview instead.
How a ZIP code is linked to a utility
ZIP codes are matched to active community water systems using three evidence types: ZIPs declared by the utility in SDWIS or UCMR 5; overlap with EPA's mapped service area; and, only as a fallback, matching reported city or county names. Each edge receives a confidence score. A primary system must reach 0.30 confidence.
A ZIP gets its own data page when its primary system has at least three UCMR 5 results, a health-based violation in the pinned 10-year window, or any lead or copper action-level exceedance on record. Other ZIP routes permanently redirect to their Census county overview. This avoids manufacturing a detailed-looking page from sparse records.
How PFAS results are compared
UCMR 5 stores individual results in µg/L; this site displays PFAS in ppt (parts per trillion, equivalent to ng/L) and lithium, lead and copper in ppb (parts per billion, equivalent to µg/L). For PFOA, PFOS, and other PFAS with an MCL, the comparison uses the highest average from a complete sampling location: two semi-annual results for groundwater or four quarterly results for surface water, with non-detects counted as zero. A highest single sample is shown but is not called a violation.
How lead and copper are compared
Lead and copper values are the 90th percentile of selected customer-tap samples for a monitoring period. Results reported only as below a laboratory limit, negative values, and values whose magnitude conflicts with the recorded unit are excluded from action-level comparisons and identified as unusable or censored.
How violations are counted
Violation counts use one pinned 10-year window across the database, prose, and tables. Health-based violations, monitoring/reporting violations, and other public-notification or report violations are counted separately and reconciled against the total during every build.
How the site checks itself
The build independently recomputes more than 1.5 million UCMR 5 and lead/copper comparisons from the raw normalized tables, then checks the comparison attributes and visible labels in rendered HTML. A mismatch stops publication.
Data vintage
EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.