In implementing the CWA, the U.S. Environmental Protection Agency (EPA) defined BMP in the federal wastewater permit regulations, initially to refer to auxiliary procedures for industrial wastewater controls.  
:...schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the pollution of waters of the United States, BMPs also include treatment requirements, operating procedures, and practices to control plant site runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.
Later the Agency added a reference to stormwater management BMPs.
:...each NPDES permit shall include conditions meeting the following requirements when applicable... (k) Best management practices (BMPs)  to control or abate the discharge of pollutants when: ... (2) Authorized under section 402(p) of the CWA for the control of storm water discharges...