Rankings & Research · PurityMap Journal
The US Cities With the Lowest Water Purity Scores (2024)
What a low Purity Score does — and does not — tell you, and how to read our national rankings without drawing the wrong conclusion.
Key takeaway
What a low Purity Score does — and does not — tell you, and how to read our national rankings without drawing the wrong conclusion.01
What the Purity Score measures
The Purity Score is computed only over the contaminants a system actually measured, scored per-contaminant against health-based references and rolled up to a 0–100 number. It is reproducible: the same inputs always give the same score. For the full method, see how the Purity Score is calculated.
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Why 'lowest' needs a caveat
A low score means more or more-severe measured exceedances — often PFAS above the 2024 federal limits, or lead. But a city that tests thoroughly can score lower than one that tests very little, simply because more was measured. Score and confidence are reported separately for exactly this reason. At the snapshot, the lowest-ranked system was the Spalding County Water System in Georgia (PWSID GA2550036) at 0 out of 100, with 5 flagged contaminants on record.
A low score is a reason to read the evidence, not a verdict. Every finding on PurityMap links to its dated EPA source.
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How to use the rankings
Open the full national water rankings to see the lowest- and highest-scoring systems, each with its metric and data cutoff, and compare against the cities with the highest Purity Scores. Then click through to a city water report to see which contaminants drove the number — and whether a certified filter addresses them.
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Health disclaimer
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 specific contaminants, consult a licensed healthcare professional, and use a certified laboratory to test your own water.
What the evidence supports
Authored analysis
The article sections above are the published interpretation for this topic, tied to the source list below.
What it does not tell us
This editorial record alone cannot determine a household’s exposure, diagnose a health condition, or replace current system-level evidence.
Methodology note
Rankings use the PurityMap Purity Score (v1, 2024-federal benchmark) over EPA UCMR5 and SDWIS inputs. The Spalding County example (GA2550036, 0/100, 5 flagged contaminants) is from the ranking snapshot dated 2026-09-16 (data cutoff 2024-12-31). No values were estimated.
Sources cited
These are the source citations published with this article. Open the data-source library to understand how PurityMap handles provenance and limitations.
- 01
PurityMap national rankings — Lowest Purity Scores in the US (2024); data cutoff 2024-12-31, snapshot 2026-09-16.
- 02
PurityMap Purity Score methodology (v1, 2024-federal benchmark).
- 03
US EPA — UCMR5 (2024) and SDWIS records, the inputs to the score. https://www.epa.gov/dwucmr/occurrence-data-unregulated-contaminant-monitoring-rule