How the grades work
Data sources
Everything on this site comes from two public U.S. EPA datasets: SDWIS (the Safe Drinking Water Information System — every public water system's violation and enforcement history) and UCMR 5 (the 2023–2025 national testing program that measured 29 PFAS "forever chemicals" plus lithium in drinking water). We refresh our copy from the EPA's published files; dates shown on each page reflect the underlying records.
Scoring
Each water system starts at 100 points:
- −15 per health-based violation in the last 5 years (MCL exceedances, treatment technique failures)
- −3 per monitoring/reporting violation in the last 5 years (capped at −15)
- −30 if any PFAS result meets or exceeds a 2024 federal limit (PFOA/PFOS: 4 ppt; PFHxS, PFNA, HFPO-DA: 10 ppt)
- −10 if PFAS was detected below the limits
90+ = A, 80–89 = B, 70–79 = C, 60–69 = D, below 60 = F. A ZIP code shows the worst grade among systems serving it.
What the grades are not
A grade is a summary of public compliance and testing records — not a measurement of the water at your tap, and not a health determination. Systems can have data gaps; small systems are tested less often. For decisions about your health, talk to your water utility (their phone number is on your bill) or a certified testing lab.
Affiliate disclosure
Some links on this site are affiliate links. If you buy a product or request a quote through them we may earn a commission, at no extra cost to you. Affiliates never influence grades — the scoring above is the whole algorithm.
Not a government site
ZIP Water Report is independent and is not affiliated with, endorsed by, or connected to the U.S. EPA or any government agency.