How grading works
Every grade on this map is arithmetic over federal records. This page shows the arithmetic.
What this site is
My Water Grade takes the U.S. EPA's own drinking water compliance records and makes them readable on a map. Nothing more. Every violation shown in a system's panel is a federal record from EPA's Safe Drinking Water Information System (SDWIS), and every grade can be traced back to those line items.
Where the data comes from
Two federal datasets, joined by each water system's federal ID (PWSID):
- Violations & enforcement: EPA's quarterly SDWA download from the ECHO program — the same records EPA uses for enforcement targeting. Data lags roughly 3–6 months because states report each quarter's violations the following quarter after verification.
- Service area boundaries: EPA's Community Water System Service Area Boundaries dataset — the polygons on the map. Some boundaries are authoritative (from utilities and states); others are modeled approximations, so edges can be imprecise.
What the grades mean
A grade summarizes a system's track record of health-based violations — weighted by how serious the contaminant is, how recent the violation is, and whether it has been fixed. It is a compliance history, not a water test.
| Grade | Meaning |
|---|---|
| A | No reported health-based violations in the scoring window |
| B | Minor or fully resolved issues |
| C | Moderate reported violations |
| D | Significant reported violations |
| F | Serious and/or unresolved violations (roughly the worst 2% nationally) |
| Insufficient data to grade |
The formula
Each health-based violation earns points; a system's score is the sum. Points = severity × status × recency.
| Factor | Values |
|---|---|
| Contaminant severity | ×10 — lead, arsenic, nitrate/nitrite, E. coli, PFAS, radionuclides
(radium, uranium), mercury, cadmium — contaminants harmful at any measurable
level or acutely dangerous ×5 — disinfection byproducts (TTHM, haloacetic acids), turbidity — chronic-exposure risks ×2 — all other health-based violations |
| Resolution status | ×3 — open, no enforcement (unaddressed) ×2 — open, under formal enforcement ×1 — resolved or archived |
| Recency | ×1 — within 3 years ×0.5 — 3–5 years ago ×0.25 — 5–10 years ago ×0 — older than 10 years (shown in history, excluded from the grade) |
Grade bands: A = 0 · B < 10 · C < 25 · D < 75 · F ≥ 75
Bands are calibrated against the national score distribution so grades mean something relative to peers. Monitoring and paperwork violations (late reports, missed filings) are excluded from the grade — a small system that files paperwork late but has clean water is not the same as one with contamination.
The reasoning behind the choices
Why do old, resolved violations still count? Because in this data, "Resolved" describes paperwork, not necessarily water. Systems exist with over a hundred health violations in five years, each individually marked resolved — a pattern of repeated violations that were administratively closed does not suggest the underlying problem was fixed. Track record predicts future performance better than current status; forgiveness in this formula is earned by time without violations, not by forms filed. A system that genuinely fixed its problem five years ago already scores near-clean under the recency decay.
Why do open violations count triple? An unfixed problem is a present problem.
Why don't paperwork violations count? Because the grade should reflect water, not administration. (One planned exception: systems that skip required testing for high-risk contaminants like lead — failure to look is not the same as looking and finding nothing, and a future update will mark those systems as unverified rather than clean.)
Structural precedent: EPA's own enforcement targeting weights health-based violations five-to-one over monitoring violations, with a multiplier for how long problems have gone unaddressed. This formula follows that structure with our own weights, which are editorial choices and published here in full.
Honest limitations
Grades reflect reported records, not water testing. EPA itself acknowledges underreporting in SDWIS. A system with no reported violations is described exactly that way — it is not a guarantee of clean water.
An A means compliance with legal limits, not purity. Legal thresholds are regulatory balancing points, not health-based purity standards. Water can be legal and still carry contaminants at levels some health organizations consider concerning.
Data lags 3–6 months by federal reporting design.
Boundaries are approximate for many systems, especially near edges. If you receive a water bill, the utility named on it serves you.
No polygon ≠ no water. Roughly 1 in 8 Americans are on private wells, which are unregulated under the Safe Drinking Water Act and are the owner's responsibility to test.
Where to verify
Every system's federal record can be checked directly against EPA's ECHO database using the PWSID shown in its panel. If you believe a record is wrong, the error is in the federal data — report it to your state drinking water program, and it will flow into our next quarterly update.
Updates
Data refreshes quarterly with EPA's SDWA release. The scoring formula on this page describes the version currently live; when weights change, this page changes with them.