How TapGraded Grades Work

TapGraded assigns one letter grade — A through F — to every active community water system in the United States. The goal is to make a large, technical public dataset legible without dumbing it down or dramatizing it. This post is the short version; the full methodology has the exact rubric and a worked example.

What the grade is made of

Every system starts at 100 points, and points are deducted from public EPA records:

Health-based violations in the last five years — an exceedance of a Maximum Contaminant Level, a disinfectant-level limit, or a treatment-technique requirement. These carry the most weight, with unresolved violations penalized more than resolved ones.
Monitoring and reporting violations — a system missed a required test or a reporting deadline. These are weighted far more lightly, because a paperwork lapse is not the same as an actual health exceedance. (Violations EPA categorizes as “Other” are counted in this monitoring bucket.)
Lead — the latest Lead and Copper Rule 90th-percentile result, scored against the 15 ppb action level and lower thresholds.
PFAS — detections from EPA’s UCMR5 monitoring, scored against the federal PFAS limits.
A currently unaddressed health violation adds a further penalty.

The remaining score maps to a letter: A is 90 and up, B is 80–89, C is 65–79, D is 50–64, and F is below 50.

What it deliberately leaves out

Only community water systems — the utilities serving residents year-round — get a grade. Schools, campgrounds, and other transient systems are out of scope, because this rubric would mislead if applied to them.
Absence of data is never scored as “clean.” If a system has no reported result for a measure, that’s stated as missing data, not counted as a pass.
The grade describes the system, not your home. Lead in particular is usually picked up in household plumbing, which no system-level grade can capture. A certified tap test is the only way to know your own number.

Why it’s reproducible

Every deduction comes from public EPA data, and the exact rules — the point values, the caps, the thresholds — are published in full. That means anyone can trace a grade back to the records behind it, and we can check a disputed grade against its source. The same data drives our rankings, and every source is listed on the data sources page.

If you think a grade is wrong

Because the method is transparent, corrections are checkable. Email contact@tapgraded.com with the system’s name or PWSID and what looks off, and we’ll re-check it against the source data.

Sources

TapGraded — “How the Tap Grade Works (Methodology)” — https://tapgraded.com/methodology
US EPA — “Safe Drinking Water Act (SDWA)” — https://www.epa.gov/sdwa
US EPA — “ECHO — Drinking Water Data Downloads” — https://echo.epa.gov/tools/data-downloads