Communities will need hundreds of billions of dollars in coming years to construct and upgrade wastewater treatment facilities, sewer systems, and other water infrastructure. To finance these efforts, they will rely heavily on low-interest loans from the Environmental Protection Agency's (EPA) Clean Water State Revolving Fund (CWSRF) program to supplement their own funds. Through fiscal year 2005, states have used their CWSRFs to provide communities over $52 billion for a variety of water quality projects. The Clean Water Act allows states to use their CWSRFs to (1) construct or improve conventional wastewater infrastructure, (2) control diffuse (nonpoint) sources of pollution such as agricultural runoff and leaking septic systems, and (3) protect federally-designated estuaries. Given the states' flexibility in determining how to spend CWSRF dollars, GAO was asked to examine (1) the extent to which states use their CWSRF dollars to support conventional wastewater treatment infrastructure versus other qualifying expenses, (2) the strategies states use to allocate their CWSRF dollars among qualifying expenses, and (3) the measures states use to ensure that their allocation strategies result in the most efficient and effective use of CWSRF dollars. EPA reviewed a report draft, providing technical comments that were incorporated.