National Pollutant Discharge Elimination System Law and Legal Definition

National Pollutant Discharge Elimination System (NPDES) is a provision of the Clean Water Act that prohibits discharge of pollutants into waters of the U.S. unless a special permit is issued by the EPA, a state, or a tribal government.

The main pollutants regulated by the NPDES include conventional pollutants and wastewater from commercial and industrial facilities, fecal coliform, oil and grease, toxic pollutants and nonconventional pollutants.

Industrial, municipal, or agricultural facilities discharging directly into surface water require NPDES permits. NPDES permits can be obtained at a state environmental protection office, or at an Environmental Protection Agency (EPA). The EPA monitors NPDES compliance with on site inspections and data review. If any provisions are not fulfilled, it can result in civil and criminal action against the violator.