Summary: GAO discussed the implementation of the Safe Drinking Water Act Program, focusing on: (1) the extent to which community water systems complied with monitoring requirements and met drinking water standards; (2) states' and the Environmental Protection Agency's (EPA) effectiveness in enforcing efforts to ensure compliance with those requirements; and (3) the impact of new drinking water requirements. GAO noted that: (1) many water systems, particularly smaller systems, were violating monitoring requirements for water quality and drinking water standards; (2) some violations were going undetected primarily due to sampling errors and deliberate falsification or manipulation of compliance data; (3) states' and EPA enforcement actions, intended to deter violations and return systems to compliance, often fell short of EPA program requirements and were frequently ineffective in achieving their objectives; (4) at the federal level, EPA lacked key data needed to determine water systems' compliance; (5) EPA did not fully implement programs that could improve compliance; (6) EPA enforcement efforts to deter noncompliance were inadequate; and (7) the implementation of new and more stringent regulatory requirements could make compliance and enforcement more difficult.