Methodology and limitations
How Tap Truth works
Tap Truth takes EPA's public drinking water records and lays them out so you can read them. It does not score systems or say whether your water is safe. It shows the federal violation history and leaves the judgment to you.
How it works
For address lookup, the app geocodes the address, tries to match the point against published EPA service-area boundaries first, and then falls back to ZIP and county lookup when no boundary match is available.
For system search, you can search by system name, city, or ZIP code, pick the correct active community water system, and view the same violation record page.
Data sources
| Source | What it provides | Snapshot | Format |
|---|---|---|---|
| EPA ECHO SDWA Downloads | Full violation history, formal enforcement actions, water sources and system metadata for public water systems. | 2026 Q1 release (records through March 2026), loaded July 2026 | CSV |
| EPA service line inventory (SDWIS) | Lead service line counts and reporting status each utility filed with EPA. | 2025 Q4 | CSV |
| Census Geocoder | Address to latitude and longitude for the lookup path. | Live service, queried at lookup time | REST |
| EPA Service Area Boundaries | Polygon boundaries used for point-in-polygon system matching when published coverage is available. | Version 2.1 (November 2025), downloaded from EPIC in February 2026 | GeoJSON |
| Census ZCTA-to-county crosswalk | ZIP to county mapping for fallback lookup when polygon data is not available. | 2020 Census | TXT |
How system pages are built
- Counts and tables cover violations that were open at any point in the last ten years. The "Full record" section counts every violation by the date it began: its summary and its list cover violations that began before the ten-year window, including any that stayed open into it, and its decade table splits the decade at the same date.
- A violation counts as resolved only when EPA lists it as resolved. Violations EPA archived without a recorded fix are counted as neither resolved nor unresolved.
- A measured level is shown only for limit violations where the reported value, its unit and the federal limit are consistent. EPA's file often mixes milligrams and micrograms, so many measured values are left out rather than shown with a wrong multiple.
- Enforcement actions are the formal actions in EPA's file (orders, penalties, compliance agreements and court cases), plus boil water orders and bans on new connections. Reminder letters and site visits are not listed.
- Water sources, and which systems buy water from which, come from EPA's facility table for active sources.
- County and state comparisons use the county of the system's mailing ZIP code.
What this tool does not do
- Does not test water quality. That requires lab analysis.
- Does not cover private wells. It only covers regulated public water systems.
- Does not use EWG's non-EPA standards.
- Does not give eligibility verdicts or safety opinions. It displays the federal record only.
- Is not a health advice or legal compliance tool.
Limitations
- Private wells are not covered because they are not regulated public water systems.
- EPA's lead service line inventory covers pipes the water system owns, usually up to the property line. Plumbing inside a home built before 1986 can still contain lead even when the system reports no lead lines.
- The data is not real-time. It comes from public EPA downloads rather than live utility feeds.
- Tap Truth uses EPA service-area boundaries first when they are available, which is more accurate than ZIP-only matching.
- Not every public system has complete boundary coverage in the published EPA data, so some addresses still require ZIP and county fallback.
- Private wells, small private utilities, and unusual service areas can still be harder to match perfectly when boundary coverage is missing.
Verification
Tap Truth is an access layer over federal data. You can verify any system directly in EPA ECHO.
View EPA ECHO drinking water data →