Water intelligence · governed snapshots
Water Quality Ranking Snapshots
Explore fixed, dated comparisons of public water systems. Every snapshot states its metric, direction, cutoff, exclusions, and limitations so the ordering can be interpreted in context.
A ranking is not a safety verdict
Each list compares one published metric for one entity class. It does not summarize everything about a system or the water at a household tap.
Latest snapshot 2026-09-16
Published snapshots
Use the metric label and direction before reading the order. Lower or higher is “better” only for that named measure, not overall water quality.
Water System comparison
Higher metric firstLowest Purity Scores in the US (2024)
Purity Score
- 1SPALDING COUNTY WATER SYSTEMSpalding County, GA · 0 / 100
- 2DAYTON PUBLIC WATER SYSTEMDayton, OH · 0 / 100
- 3VERO BEACH, CITY OFVero Beach, FL · 31 / 100
Scores reflect only measured contaminants; a city with sparse monitoring can score higher simply because less was tested. This is not an overall safety ranking.
Open snapshot and methodologyWater System comparison
Higher metric firstHighest Purity Scores in the US (2024)
Purity Score
- 1SAN DIEGO, CITY OFSan Diego, CA · 100 / 100
- 2ROSWELL MUNICIPAL WATER SYSTEMRoswell, NM · 100 / 100
- 3CITY OF BUCKEYE TARTESSO WATER SYSTEMBuckeye Tartesso, AZ · 100 / 100
A high score reflects a clean measured record, not proof that every possible contaminant is absent. Monitoring depth varies by system.
Open snapshot and methodologyWater System comparison
Higher metric firstLargest US Water Systems by Population Served
Population served
- 1NEW YORK CITY SYSTEMNew York City, NY · 8 271 000 served
- 2LOS ANGELES-CITY, DEPT. OF WATER & POWERLos Angeles, CA · 3 875 566 served
- 3CITY OF HOUSTONHouston, TX · 2 970 543 served
Population figures are as reported to EPA and can lag real service-area changes. Size is not a quality signal.
Open snapshot and methodologyWater System comparison
Lower metric firstU.S. Cities Where PFAS Exceeds the 2024 Federal Limit
PFOS, highest monitored result
- 1EMMAUS BOROUGH PUBLIC WATEREmmaus, PA · 153.0 ng/L (limit 4.0)
- 2CITY OF GRAND PRAIRIEGrand Prairie, TX · 82.0 ng/L (limit 4.0)
- 3CITY OF OXFORDOxford, MS · 72.2 ng/L (limit 4.0)
Figures are monitored public-system results for the stated period, not necessarily current treated water. Utilities may treat before delivery. A result above a limit is a regulatory exceedance, not an individual health verdict.
Open snapshot and methodologyWater System comparison
Lower metric firstU.S. Cities Where Lead Exceeds the Federal Action Level
Lead, 90th-percentile monitored result
- 1DAYTON PUBLIC WATER SYSTEMDayton, OH · 470.0 µg/L (action level 15)
- 2SMITHFIELD CITYSmithfield, UT · 46.0 µg/L (action level 15)
- 3NORTHSHORE UTILITY DISTRICTNorthshore District, WA · 36.0 µg/L (action level 15)
The action level is a treatment trigger, not a health-based limit; there is no known safe level of lead. Results are monitored public-system values for the reporting period, and household plumbing can add lead at the tap regardless of the system result.
Open snapshot and methodologyHow to read a ranking
Read the metric
The title alone is not enough. Confirm what is measured and whether lower or higher values appear first.
Check the date
Results belong to the stated snapshot and data cutoff. They are not a live status indicator.
Inspect exclusions
Missing or incomparable records stay excluded and are documented rather than silently treated as favorable results.
Comparable does not mean complete.
Ranking snapshots compare water systems, not cities or households. They never replace a system report, a city-resolution check, or a certified tap test.
Methodology and governance
PurityMap publishes only fixed ranking snapshots supplied by the governed data layer. The frontend does not sort live values into new rankings, relabel supplier results as city results, or fill missing observations.
Review the analysis method →