Under the federal Clean Water Act, POTWs are not just the wastewater treatment plants themselves. They include a wide array of other infrastructure necessary for collecting, transporting and treating wastewater containing domestic or sanitary sewage and sludge or biosolids resulting from the wastewater treatment process.

While the term "clean water infrastructure" includes facilities to control combined sewer overflows (CSOS) from combined sanitary and storm sewer systems and separate sanitary sewer overflows (SSOs), these facilities are not considered as POTWS. Both CSOs and SSOs result from storm events, which cause high volumes of water that overflows from older sewage collections systems.

Reproduced courtesy from the Association of Metropolitan Sewerage Agencies (AMSA) - www.amsa-cleanwater.org. The Cost of Clean is also available on AMSA's web site or by contacting AMSA's National Office at (202) 833-AMSA.