Groundwater quality data for 472 domestic well-water samples were retrieved from the USGS National Water Information System (NWIS) database and combined with descriptive information on the sampled well locations. The NWIS data for a sample, collected on the selected date, were averaged into a single record (one per well), and rounded according to USGS protocols. For evaluation and reporting, the water-quality data were further combined with physical attributes and classified by lithology, topographic position, physiographic province, region, redox, and pH (as standalone matrix, one row per well). A second data matrix file incorporating minimum reporting levels for censored and low-reported values (set to 0.99X highest common reporting level) was generated for statistical analysis. The two water-quality matrix files, in comma delimited format (.csv) plus a third file that has complete descriptive information for all the water-quality and physical parameters constitute the primary products of the data release.