Data Sources

Every number traces back to a public record.

We don't make up averages or aggregate someone else's aggregations. Each fact on this site is sourced from a specific federal or state dataset, linked below. If you click into a system page, the data provenance shows up next to every measurement — source, year, and sample count.

What we ingest

EPA UCMR 5 — PFAS & Lithium Occurrence Data

Source ↗

Per-system PFAS detections at every U.S. PWS serving >3,300 people, 2023–2025.

Coverage: ~10,300 systems · 30 analytes · finished water at entry points
License: U.S. federal public domain (17 USC § 105)
Updated: Sampling period closes Q4 2025; we re-pull quarterly.

Utility Consumer Confidence Reports (CCRs)

Source ↗

Annual contaminant disclosures every U.S. community water system is legally required to publish (40 CFR § 141.151–155). Our extraction pipeline transcribes the PDFs into structured facts.

Coverage: ~500 systems today, scaling to all ~50,000 U.S. CWSes
License: Facts in CCRs are not copyrightable (Feist v. Rural). Our structured, normalized version is © The Water Map, CC BY 4.0.
Updated: Annually — utilities publish for the prior calendar year by July 1.

EPA SDWIS — Safe Drinking Water Information System

Source ↗

The master inventory of every public water system in the U.S. — PWSID, system name, population served, source-water type, treatment facilities, violations, cities served.

Coverage: ~150,000 active systems · quarterly refresh
License: U.S. federal public domain (via EPA ECHO)
Updated: Quarterly snapshot from ECHO Exporter.

EPA Maximum Contaminant Levels (MCLs)

Source ↗

The legal limits we compare every measurement against. Updated when EPA finalizes new rules (e.g. PFAS NPDWR, April 2024).

Coverage: All federally regulated drinking-water contaminants
License: U.S. federal public domain
Updated: Tracks EPA's published rules; reflects PFAS NPDWR 2024 limits.

State Open-Data Portals

Source ↗

State primacy-agency sampling data for the post-2019 gap UCMR/SYR4 don't cover.

Coverage: California (DRINC), Texas (TCEQ DWW), New York (Open Data), Florida & Massachusetts DEP — added as we ingest them.
License: Per each state's open-data terms (typically permissive with attribution).
Updated: Rolling — added per state.

What we don't use, and why

EWG Tap Water Database

It re-publishes the same EPA + state data we already ingest directly. We go to the source.

Proprietary aggregators (SimpleLab, TapScore, etc.)

Commercial datasets that wrap public data behind paywalls. We can hit the originals for free.

Found something off?

Public data isn't always clean. Utilities mistype numbers, units get swapped, samples get misclassified. If a value on this site disagrees with the source PDF or with what your utility tells you directly, that's worth knowing about.

Email a correction

The Water Map is independent. We are not affiliated with EPA, any state agency, or any water utility. We publish their disclosed data in a more usable form and compare it to current EPA standards.