Data sources
Everything on TapGraded is built from public federal data and a small curated reference table. No figure is invented; each dataset below is linked to its origin so any number can be traced back to its source.
Data vintage: EPA Safe Drinking Water Act data (2026 Q2) downloaded 2026-07-16; EPA UCMR5 occurrence data downloaded 2026-07-16. Data refreshes on EPA’s quarterly cadence.
| Source | What it provides | Scale | License |
|---|---|---|---|
| EPA ECHO — Safe Drinking Water Act (SDWA) quarterly bulk | Water systems, violations and enforcement actions, Lead & Copper Rule (LCR) samples, facilities, sanitary site visits, service-area geography, and SDWIS reference codes. | 434,040 water systems (49,378 active community systems graded); 927,415 LCR samples; 1,554,832 facilities; 2,495,249 site visits. | US federal government data — public domain. |
| EPA UCMR5 — occurrence data (PFAS) | Fifth Unregulated Contaminant Monitoring Rule sampling results, including the per-system PFAS detections used for the PFAS part of the Tap Grade. | 1,928,117 monitoring results. | US federal government data — public domain. |
| US Census Bureau — 2025 Gazetteer (ZCTAs) | ZIP Code Tabulation Area centroids used to resolve a ZIP code to a place for the ZIP lookup. | 33,791 ZCTAs. | US federal government data — public domain. |
| GeoNames — US postal codes | City / state / county enrichment for ZIP geo-joins, filling gaps the Census ZCTA file leaves (e.g. non-ZCTA USPS ZIPs). | US postal-code dataset. | Creative Commons Attribution 4.0 (CC-BY 4.0) — attribution required. |
| TapGraded — curated contaminant reference | A hand-built reference table of regulated contaminants — MCL / MCLG values, health effects, common sources, and removal technologies — each verified against the EPA regulation pages it cites. | 43 contaminants. | Compiled by TapGraded from EPA regulations (public domain source data). |
Attribution
Postal-code geography is enriched using data from GeoNames, © GeoNames, licensed under a Creative Commons Attribution 4.0 International License (CC-BY 4.0).
How the data is used
The EPA Safe Drinking Water Act and UCMR5 datasets drive the Tap Grade (see the methodology for the exact rubric) and every utility, city, and state page. The Census and GeoNames geography datasets are used only to turn a ZIP code into a place for the ZIP lookup — they never affect a grade. The curated contaminant reference supplies the regulatory limits and health-effect summaries shown on contaminant pages.
Source: EPA SDWIS/ECHO + UCMR5, US Census, GeoNames (this page) · Data as of 2026 Q2 (downloaded 2026-07-16)