How Safe are United States Public Water Supply Systems?

Abstract:

With ~90% of the U.S. population obtaining water from public water supply (PWS) systems, assessing the safety of these water systems is critical to public health. Here we evaluated spatiotemporal trends in health-based violations of community water systems (CWSs) under the Safe Drinking Water Act (SDWA) from 1980 to 2018 in response to evolving drinking water regulations. Results show that CWSs accounted for ~35% of all active PWSs and served ~94% of the U.S. population. While ~85% of CWSs are relatively small systems relying on groundwater, the remaining fraction of CWSs are relatively larger surface water systems, serving ~70% of the population. About 60% of all CWSs were subject to at least one health-based violation during 1980 – 2018, serving ~200 million people, ~70% from surface water and ~30% from groundwater. Violations of SDWA regulations in 2018 were dominated by total coliform, followed by disinfectants and disinfection byproducts (DBPs), and inorganic contaminants. Surface water system violations were dominated by DBPs, followed by total coliform, and surface water treatment rule noncompliance whereas groundwater system violations were dominated by total coliform, followed by inorganics (e.g., metals) in 2018. Spikes in violations occurred after regulatory changes, e.g. ~2005 and ~2015 adoption of Stage 1 and Stage 2 DBP rules and 2006 lowering of arsenic maximum contaminant level. Spatial analysis focused on maps of inorganic contaminant violations as an example. Arsenic violations peaked in 2006 – 2008, showing widespread impacts in California, Arizona, parts of Texas, Oklahoma, and the northeastern U.S. The 2015 – 2017 arsenic map shows reductions in arsenic violations in the northeast, Arkansas, and Arizona. The largest impacts of fluoride violations were in the High Plains of Texas and mid-regions of Oklahoma and some isolated regions in southern California and Arizona. Populations impacted by nitrate contamination were primarily in California, the U.S. High Plains, the Great Lakes region, and the north east. Much of the inorganic contamination is attributed to natural, geogenic sources. The Safe Drinking Water Information System allows tracking spatiotemporal variability in water quality issues that can be linked to various sources of contamination and treatment options across the U.S.