What you're looking at
PurityMap's national rankings order water systems by their Purity Score — a reproducible 0–100 number computed only over the contaminants a system actually measured, scored against health-based references. The Highest Purity Scores list (data cutoff December 31, 2024; snapshot September 16, 2026) shows the systems with the cleanest measured records on file. Only cities with both a computed score and a resolved serving system are eligible, so 3,755 systems were set aside — a high position reflects the data available, not a contest of every US city.
At the top of the list
At the time of the snapshot, the top-ranked system was the City and Borough of Juneau, Alaska (PWSID AK2110342, serving about 38,526 people) at 100 out of 100, followed by Scottsboro Water, Sewer & Gas in Alabama (AL0000729, about 22,200) and the Walnut Hill Water Authority, also in Alabama (AL0001289, about 14,127). Many systems share the same 100/100, so the exact order among them reflects tie-breaking rather than a meaningful gap. These are mostly mid-size utilities, not the largest metros.
Why a perfect score needs a caveat
A 100 does not mean every possible contaminant is absent. It means that across the contaminants this system tested, none exceeded its health-based reference. A system that monitors a narrow set can post a perfect score simply because less was measured — which is why PurityMap reports confidence separately from the score. Read a high score as 'a clean record so far,' not as a finish line.
A high Purity Score reflects a clean measured record, not proof that every contaminant is absent. Monitoring depth varies from system to system.
What a system score can't tell you about your tap
Even a top-ranked system describes treated water leaving the utility, not the water at your kitchen sink. Lead in particular usually enters through a home's own service line or fixtures, so a system's clean record does not rule out lead at an older tap. Confirm your supplier on your utility bill, and treat the ranking as a starting point for your address rather than a conclusion about it.
How to use the ranking
Open the full national water rankings to see all 25 systems with their scores and data cutoff, then click any system through to its city water report to see which contaminants were measured and when. To understand what drives the number, read how the Purity Score is calculated, or compare against the cities with the lowest Purity Scores. For your own city, search its report and check the PFAS and lead findings directly.
This article explains a scoring method built on public EPA monitoring data. It is not medical advice and does not declare any water fit or unfit for a specific person. For health questions about lead, PFAS or other contaminants, consult a licensed healthcare professional and, for your own address, use a certified laboratory test.