Water pollution degrades surface waters making them unsafe for drinking, fishing, swimming, 
and other activities. As authorized by the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into waters of the United States.
Point sources are discrete conveyances such as pipes or man-made ditches. Individual homes that are connected to a municipal system, use a septic system, or do not have a surface discharge do not need an NPDES permit; however, industrial, municipal, and other facilities must obtain permits if their discharges go directly to surface waters. In most cases, the NPDES permit program is administered by authorized states.
Since its introduction in 1972, the NPDES permit program is responsible for significant improvements to our Nation’s water quality.
Learn more about NPDES on the US EPA website.
Source: EPA.gov