How We Grade Water Quality
The grading system behind every MyWaterIQ report — what counts against a water system, what doesn't, and why we grade against enforceable standards instead of aspirational goals.
Every county and community page on MyWaterIQ carries a letter grade, A through F. This article explains where that grade comes from, so you can judge for yourself how much weight to give it. The short version: we grade against the standards that carry legal force, using the federal enforcement database — and nothing else.
Where the data comes from
Every number on this site comes from the EPA's Safe Drinking Water Information System (SDWIS), exported from EPA ECHO — the same federal database that regulators, utilities, and public health officials rely on. It carries violations and enforcement records, lead and copper test results, system characteristics, and state sanitary survey findings. We refresh our database quarterly as new EPA exports become available.
We do not use Consumer Confidence Reports. CCRs are self-reported by utilities and not independently verified; SDWIS is federally mandated and audited.
The standard versus the goal
Federal drinking water rules contain two different kinds of number, and which one you grade against changes everything.
An MCL (Maximum Contaminant Level) is the legally enforceable limit. Exceeding it puts a utility in violation of federal law and obliges it to notify customers and take corrective action. An MCLG (Maximum Contaminant Level Goal) is an aspirational target — set at zero for many contaminants, including lead. Because the goal is zero, virtually every water system in America can be made to look dangerous when measured against it, which is exactly how some sites use it.
We grade on actual MCL violations and measured lead results, never on MCLG-based detections. If a system is breaking an enforceable limit, that counts against it. If it merely registers a detection above an unenforceable goal of zero, it does not.
Lead: what 15 ppb actually means
SDWIS reports lead as a 90th-percentile result across sampled taps, which we convert to parts per billion. The federal action level is 15 ppb — and it is worth being precise about what that number is. It is a treatment trigger, not a legal maximum: a system at or above it is required to take corrective action. It is not an MCL, and it is not a safety line for any individual home.
Our grading reflects that. Lead at or above the action level costs a system heavily; lead between 5 and 15 ppb costs it a smaller amount. And a reported result of zero means not detected — the sample fell below the laboratory detection limit — so we render it as "Not detected," never as "0 ppb."
PFAS: the newest enforceable limits
EPA set the first federal PFAS limits in 2024: 4 parts per trillion for PFOA and PFOS, and 10 ppt for PFHxS, PFNA, and GenX. A system exceeding a federal PFAS limit takes one of the largest deductions in our system. But PFAS monitoring was only required of larger systems, so many communities have never been sampled. Where that's the case, the page says not tested — we never treat absence of testing as evidence of clean water.
How the score becomes a grade
Each system starts at 100 points and takes deductions for what the record shows: open health-based violations, health-based violations in recent history, lead against the action level, copper against its action level, PFAS above a federal limit, and significant deficiencies found in state inspections. A is 90 or above, B 78, C 62, D 45, and F is anything below that.
One rule matters more than the exact point values: a system we cannot verify cannot earn an A. If lead or PFAS has never been measured, the grade is capped one below the top — because a system nobody examined should never outrank one that was tested and found clean. Absence of testing is never penalised either; sampling requirements are outside a utility's control. The full deduction table, thresholds, and every caveat are published on our methodology page.
What a grade is not
A grade summarises a system's federal compliance record. It is not medical advice, and we don't make medical recommendations — if you have specific health concerns about your water, talk to a professional. What we can give you is the record itself: start with your state, drill down to your county and community, and see exactly what the grade was based on.