In January 2001, the Environmental Protection Agency (EPA) promulgated a new regulation for arsenic in drinking water, as required by 1996 Safe Drinking Water Act Amendments. The rule set the legal limit for arsenic in tap water at 10 parts per billion (ppb), replacing a 50 ppb standard that was set in 1975, before arsenic was classified as a carcinogen. The arsenic rule was to enter into effect on March 23, 2001, and public water systems were given until January 23, 2006, to comply. When issuing the rule, EPA projected that compliance could be costly for some small systems, but many water utilities and communities expressed concern that EPA had underestimated the rule's costs. Subsequently, EPA postponed the rule's effective date to February 22, 2002, in order to review the science and cost and benefit analyses supporting the rule. In October 2001, EPA affirmed the 10 ppb standard. The compliance date remained unchanged, and the new standard became enforceable for water systems in January 2006. With the arsenic regulation in place, Congress and EPA have focused on how to help communities comply with the new requirements. In the 109th Congress, bills have been introduced to establish small system grant programs and to provide more compliance flexibility and technical assistance to small systems. This report reviews issues surrounding the arsenic rule and related congressional and EPA actions.