Source transparency
Water Hardness Data Sources
The dataset combines treated-water reports, public water system records, USGS monitoring, and clearly labeled fallback estimates.
Source Categories
Treated-water reports
State compliance labs, annual water quality reports, and utility-published treated-water values.
EPA SDWIS
Public water system identifiers, system metadata, service populations, and system matching context.
USGS monitoring
Water-quality observations used when direct treated-water readings are unavailable.
Fallback estimates
Nearby, county, or state-level values used only when stronger local evidence is not available.
Current Source Mix
| ZIP source label | ZIP count |
|---|---|
| USGS monitoring | 11,136 |
| Annual Water Quality Report | 11,119 |
| Nearby estimate | 6,782 |
| California treated-water report | 1,404 |
| County average estimate | 447 |
| Michigan utility report | 372 |
| State average estimate | 122 |
| Unknown source | 7 |
Example Source-Backed Systems
How to Read a Source Label
A treated-water label means the value is closer to what a municipal customer receives after treatment. A USGS label means the value is based on public monitoring data. Estimated labels are useful directional readings, but they should be confirmed before equipment sizing.