Comparative analysis of service area boundaries and disparities in drinking water quality

Service area boundaries are the geographic delineation of a community water system’s (CWS) customer base. Lack of consistent and precise service area boundaries may affect how measures of water quality are geospatially assigned in academic or regulatory work, potentially hindering our ability to locate and accurately characterize disparities in drinking water provision. Though it is generally understood that more accurate boundaries would improve the analytical precision of drinking water quality analyses, it is unclear how the choice of boundary representations would impact conclusions of empirical analyses or the potential magnitude of bias. This paper aims to fill this gap by summarizing a set of novel drinking water quality metrics for arsenic, bacterial detection, disinfection byproduct formation, lead, nitrates, PFAS, and health-based violations of the Safe Drinking Water Act. We compare these drinking water measures across service area assignment methods including the use of county served, zip codes served, the EPIC/SimpleLab dataset, boundaries created by the U.S. Geologic Survey, and a national data layer produced by EPA’s Office of Research and Development. Conclusions regarding the presence of a disparity depend on the service area boundary selected for at least one demographic group for six of seven drinking water quality measures in this analysis. This paper helps to motivate the importance of producing, maintaining, and updating a high-quality, nationally consistent geodatabase of drinking water system service areas.