Joint Outfall System Water Reclamation Plants

Seventeen of the 24 independent districts in the Sanitation Districts' partnership have joined together to share a regional, interconnected sewerage system called the Joint Outfall System (JOS). 

These 17 Sanitation Districts serve 73 cities and unincorporated areas of Los Angeles County. The JOS provides the benefit of local control and the advantage of a shared regional sewerage system.

The JOS covers approximately 660 square miles, from the foothills of the San Gabriel Mountains in the north to San Pedro Bay in the south, and from the Los Angeles city limits on the west to the Los Angeles County border on the east.

The JOS includes the main Joint Water Pollution Control Plant (JWPCP) in Carson and six satellite water reclamation plants (WRPs), built near rivers to allow for the disposal of the treated water that is not reused.

The six WRPs are:

Approximately two-thirds of the wastewater in the JOS is treated at the JWPCP but is not utilized for reuse at this time since the addition of advanced treatment is required. The remaining one-third is treated at the WRPs and is available for reuse.

Organic materials removed at the WRPs, along with certain industrial waste flows, are conveyed by large trunk sewers to the JWPCP for treatment.


A map of the Joint Outfall System, showing the 17 independent Districts, large trunk sewers, 6 Water Reclamation Plants and the JWPCP in Carson.


An aerial photograph of the JWPCP, with the alignments of the 1937 and 1958 tunnel routes indicated by the dotted lines.