Arsenic Drinking Water Violations Decreased across the United States Following Revision of the Maximum Contaminant Level.

Arsenic poses a threat to public health due to widespread environmental prevalence and known carcinogenic effects. In 2001, the US EPA published the Final Arsenic Rule (FAR) for public drinking water, reducing the maximum contaminant level (MCL) from 50 to 10 μg/L. We investigated impacts of the FAR on drinking water violations temporally and geographically using the Safe Drinking Water Information System. Violations exceeding the MCL and the population served by violating systems were analyzed across the conterminous US from 2006 (onset of FAR enforcement) to 2017. The percentage of public water system violations declined from 1.3% in 2008 to 0.55% in 2017 ( < 0.001, slope = -0.070), and the population served decreased by over 1 million ( < 0.001, slope = -106 886). Geographical analysis demonstrated higher mean violations and populations served in certain counties rather than evenly distributed across states. The decline in violations is likely due to the adoption of documented and undocumented treatment methods and possibly from reduced environmental releases. Considering other studies that have shown decreased urinary arsenic levels in the population served by public water systems since the new standard, it may be inferred that the FAR is facilitating the reduction of arsenic exposure in the US.