Dataset coverage
U.S. Water Hardness Dataset
Coverage details for the public lookup powering ZIP, city, state, map, and water-system pages.
Last updated March 9, 2026.
31,389
ZIP codes
27,122
Cities
48,068
Public water systems
51
States and DC
Data Quality Summary
4,846
treated-water systems
26,311
USGS-sourced systems
7,351
estimated ZIP readings
Water System Source Counts
| Source | Systems |
|---|---|
| USGS monitoring | 26,311 |
| Nearby estimate | 13,282 |
| Annual Water Quality Report | 4,539 |
| County average estimate | 3,535 |
| California treated-water report | 290 |
| State average estimate | 94 |
| Michigan utility report | 17 |
High-Signal System Examples
New York City System
NY7003493 - New York
65 PPM - Annual Water Quality Report
Los Angeles-City, Dept. Of Water & Power
CA1910067 - California
112 PPM - California treated-water report
City Of Houston
TX1010013 - Texas
135 PPM - Annual Water Quality Report
Chicago
IL0316000 - Illinois
148 PPM - Annual Water Quality Report
Mwra
MA6000000 - Massachusetts
8 PPM - Annual Water Quality Report
Mdwasa - Main System
FL4130871 - Florida
219 PPM - Annual Water Quality Report
Dataset Use and License
The WaterHardness.org public lookup and dataset metadata are free to access. Please cite WaterHardness.org and link to this dataset page when referencing the compiled lookup. Bulk redistribution, automated extraction, or commercial reuse requires written permission. Underlying public records remain subject to the terms of their original sources.
Use the Public Lookup
The dataset is exposed through ZIP, city, state, map, and water-system pages. For bulk or partnership questions, use the contact form on the mission page.