Water quality trading is a market-based tool for achieving improved water quality. To offset its pollutant discharges, an entity required to control a pollutant in a watershed can trade water quality credits with another entity in the same watershed to lower its pollution-control costs. Water quality trading can enhance pollution reduction efforts while offering flexibility and cost savings to regulated municipalities and industries. This trading has been effective at reducing water pollution in communities throughout the United States and may offer a blueprint for policymakers to create more efficient water systems that provide safe water access to the entire community.