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Sanitation Districts of Los Angeles County

After World War I, the population in Los Angeles County began exploding at a rapid rate and a regional sewerage system and infrastructure was needed to handle this growth. The Sanitation Districts of Los Angeles County were formed in 1923 when the Sanitation District Act was adopted by the State Legislature.

Before Wastewater Treatment
Early in Los Angeles’ history, wastewater was managed very differently than it is today.

When populations were small enough, like Los Angeles in the late 1800s, wastewater was collected in buckets and put into agricultural fields or into rivers and streams.

Sanitary Sewers
As cities grew, and medical research progressed, people began to understand the health consequences of throwing their untreated waste into fields and rivers. Cities began to build independent sewerage systems to convey, adequately treat and dispose of their wastewater. Because of this, life expectancy has nearly doubled with the eradication of waterborne diseases. As a matter of fact, the British Medical Journal asked its readers what they viewed as the greatest medical advance of the past 150 years, and its readers selected improved sanitation over all other medical achievements, such as the development of antibiotics and anesthesia.

Today’s Wastewater Systems
Today, there are two major regional wastewater treatment systems in Los Angeles County. The Sanitation Districts manage a wastewater treatment system serving over 5 million people in 78 of the 88 cities in Los Angeles County, plus unincorporated county areas. The Sanitation Districts’ system includes 11 wastewater treatment plants, two tunnels extending from Carson to White Point on the Palos Verdes Peninsula, and four outfall pipelines that run along the ocean floor and discharge treated wastewater offshore.

The other major sewerage system is managed by the City of Los Angeles. It includes the Hyperion Treatment Plant, Donald C. Tillman Water Reclamation Plant, Los Angeles-Glendale Water Reclamation Plant, and Terminal Island Treatment Plant. The city’s system also includes two ocean outfalls, one in Santa Monica Bay and the other in Los Angeles Harbor.

Organization and Governance
The Sanitation Districts are a partnership of 24 independent special districts to provide both wastewater and solid waste management services.

Each District is a separate political entity with its own revenues, expenses and board of directors. The boards of directors are, in most cases, comprised of the mayors of each city in the District and the chair of the county Board of Supervisors (if any unincorporated county area falls within a District's boundaries).

The Sanitation Districts were established not by political boundaries, but by watershed areas in order to take advantage of gravity in transporting wastewater. Consequently, a city may lie in more than one Sanitation District.

Click here to go to the Sanitation Districts’ website.


In the early days of Los Angeles, wastewater was simply thrown into fields.


Scientists like Dr. Louis Pasteur and Dr. Joseph Lister discovered disease-carrying bacteria and the link between humans and water-borne diseases.


Copy of the original 1925 Bond Sale Map issued to fund the County Sanitation Districts’ regional sewerage system.