The Clean Water State Revolving Fund (CWSRF) is a self-perpetuating loan assistance authority for water quality improvement projects in the United States. The fund is administered by the Environmental Protection Agency and state agencies. The CWSRF, which replaced the Clean Water Act Construction Grants program, provides loans for the construction of municipal wastewater facilities and implementation of nonpoint source pollution control and estuary protection projects. Congress established the fund in the Water Quality Act of 1987. Since inception, cumulative assistance has surpassed US$153.6 billion as of 2021, and is continuing to grow through interest earnings, principal repayments, and leveraging. Revolving structure All 50 states, plus Puerto Rico operate a CWSRF. The 51 CWSRF programs function like environmental infrastructure banks by distributing low interest rate loans for water quality projects. Loan repayments are recycled back into individual CWSRF programs. States can only use the funds to make loans, purchase local debt, or issue financial guarantees. They cannot make grants or otherwise dissipate the capital in their funds. Principal repayments plus interest earnings become available to finance new projects, allowing the funds to "revolve" over time. States can also increase their CWSRF financing capacity by issuing CWSRF-backed revenue or general obligation bonds. As of 2007, 27 states have leveraged their programs in this way, raising an additional $20.6 billion for important water quality projects. The 51 funds are capitalized in part by federal and state contributions. For every dollar contributed by the federal government, states contribute 20 cents. As of 2017, the cumulative federal appropriation to the 51 CWSRF programs had reached over $42 billion, with corresponding state contributions of $84 billion. Financial leveraging techniques conducted by state funds had snowballed federal and state contributions into $153 billion in 2021. States are responsible for the operation of their CWSRF program. Under the CWSRF, states may provide various types of assistance, including loans, refinancing, purchasing, or guaranteeing local debt and purchasing bond insurance. States may also set specific loan terms, including interest rates from zero percent to market rate and repayment periods of up to 30 years. States have the flexibility to target financial resources to their specific community and environmental needs. States may customize loan terms to meet the needs of small and disadvantaged communities, or to provide incentives for certain types of projects. Beginning in 2009, Congress authorized the CWSRFs to provide further financial assistance through additional subsidization, such as grants,