A one-pipe sewer system in which a single pipe collects both sewage and stormwater. In dry weather, all flow goes to a wastewater treatment plant. During wet weather, some flow may be diverted to CSO treatment facilities for storage and/or treatment. In heaviest rainfall, combined sewage flow may be discharged directly to streams
A system of sewers designed to collect and convey wastewater and runoff from urban areas to the receiving stream or to a treatment plant if one is available. This is an old style of providing sewer service and drainage, and was discontinued in Edmonton the late 1950s in favour of separate storm and sanitary sewers.