The United States (U.S.) Environmental Protection Agency (EPA) is directed by the Safe Drinking Water Act (SDWA) to annually report on public water system (PWS) compliance in the United States. To meet this requirement, EPA's Office of Enforcement and Compliance Assurance (OECA) publishes the annual National Public Water Systems Compliance Report (Report) summarizing the incidence of significant violations, which include all health-based violations and a subset of other violations, as shown in Table A-1. The Report for 2011 documents that, while the majority of the U.S. population served by PWSs receives safe drinking water, many PWSs incurred significant violations of federal drinking water quality standards. The number of PWSs with significant violations decreased from 39,716 in 2010 to 37,631 in 2011.