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Joint Outfall System

Seventeen of the 24 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 and over 5 million people. The JOS provides the benefit of local control and low costs that come from a large, 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 Pacific Ocean and 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, which is the largest plant in the system, and six satellite water reclamation plants (WRPs), built throughout the county to produce recycled water throughout the JOS.

The six Water Reclamation Plants (WRP) are:

Approximately two-thirds of the wastewater in the JOS is treated at the JWPCP and is too salty for reuse without costly advanced treatment. The remaining one-third is treated at the WRPs and is available for reuse.

Organic materials removed at the WRPs and the saltier wastes from industry are transported by larger “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.