Antioch Brackish Water Desal Project

Antioch’s Need for Desalination

The City of Antioch’s current water supply system serves over 112,000 people within a 28.8 square-mile service area. The main sources of water for the City include water pumped from the San Joaquin River under the City’s senior (pre-1914) water right, and purchases from the Contra Costa Water District (CCWD). The quantity and quality of the water at the City’s San Joaquin River intake is impacted largely by factors outside of the City’s control (e.g. other delta projects, climate change, sea level rise, and state water project operations). The amount used from each source depends on the time of year and the type of year (dry or wet). The City uses river water as much as possible, because it is less expensive than water purchased from CCWD. However, over the years as the salinity of the river water has increased steadily, the City has been forced to purchase more water from CCWD as shown on the graph below.

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The City of Antioch’s Brackish Water Desalination Project is being implemented to provide the City’s water supply reliability, provide operational flexibility while reducing costs, especially during droughts and with future proposed changes in Delta water management. The Project will allow the City to use water from the river year-round, even when the salinity is above levels normally treated at the existing conventional Water Treatment Plant.

The Brackish Water Desalination Project is an important component to the City of Antioch’s long-term strategy to improve its water supply reliability by diversifying its supply sources. This strategy will allow the City to reduce its dependence on higher-cost CCWD purchased water that is vulnerable to droughts, natural disasters and regulatory restrictions. Depending on drought conditions, the plant will account for over half of all water generated in the City during certain months of the year and about 30% on an annual basis.

The main Project objectives include:

  • Improve water supply reliability and water quality for customers.
  • Develop a reliable, drought-resistant water supply to reduce the City’s dependency on purchased water supplies by preserving the value and maximizing the use of the City’s pre-1914 water rights.
  • Minimize project capital costs and reduce construction impacts by maximizing the use of existing infrastructure.
  • Implement a cost-effective project that provides for operational flexibility and allows the City to quickly respond to changes in source water quality, emergencies, and changes associated with climate and California Bay-Delta conditions.

What is Brackish Water Desalination?

Desalination is the process of removing minerals and salts from water to produce a purified water. This is achieved by pushing water at a high pressure through reverse osmosis (RO) membranes (semipermeable membrane) to remove salt and other minerals.

The source water for desalination can come from a variety of sources including seawater, agricultural run-off, salty groundwater, or other brackish water sources. Brackish water refers to water that has higher concentrations of chlorides (salinity) and total dissolved solids (TDS) than freshwater, but is not as salty as ocean water. Ocean water has approximately 35,000 mg/L of TDS, while brackish water can range from 1,000 to 10,000 mg/L of TDS.

At certain times of year, the waters near the City of Antioch are considered brackish when San Joaquin River flows decrease and the salty Bay waters reach further upstream. Because brackish water has lower concentrations of TDS and nitrates, less energy is needed to push the water through the RO membranes. Brackish water desalination can produce potable water supply at less than half the energy usage of seawater desalination.

Before the finished water is ready to be pumped into the water system and distributed to customers, minerals are reintroduced into the water to make it compatible with other water supplies.

Project Description

The Antioch Brackish Water Desalination Project, which utilizes existing infrastructure to the extent possible, includes the construction of new desalination facilities and associated infrastructure, in order to improve the City’s water supply reliability and operational flexibility. Once constructed the desalination facility, located at the existing water treatment plant, will provide for 6 million gallons per day of capacity (producing up to 5,500 acre feet per year (ac-ft/yr),  helping the City reduce its purchases of more expensive CCWD water.

Project Components

The Antioch Brackish Water Desalination Project consists of the following components:

  • New river intake pump station to replace the existing San Joaquin River intake pump station. The pump station will consist of three 8 mgd pumps (16 mgd firm capacity) each with a fish screen that meets the protective criteria of the California Department of Fish and Wildlife and National Marine Fisheries Service.
  • New 3,000 foot pipeline connecting the City’s existing raw water pipeline to the City’s Water Treatment Plant to allow a direct connection and maximize the use of existing infrastructure
  • New 6 mgd desalination facility (reverse osmosis, post-treatment systems, chemical feed and storage facilities, brine conveyance facilities, and other associated non-process facilities).
  • Approximately 4.3 miles of a new brine disposal pipeline to convey discharge brine the Delta Diablo Wastewater Treatment Plant for disposal into the San Joaquin River through an existing outfall. Discharge of brine water into the San Joaquin River will result in minor local increases in salinities that are within the tolerance range of native species.

Optimizing Use of Existing Infrastructure

The Project’s design optimizes the use of existing infrastructure to reduce overall construction related impacts to the community as well as overall project costs. Existing facilities that are utilized in this project include the:

  • Existing raw water pipeline, from the San Joaquin River intake to the WTP, will be used to convey river water to the City’s water treatment plant.
  • Existing Water Treatment Plant processes will provide for the pretreatment of the raw water prior being routed to the new advanced treatment facility (reverse osmosis).
  • Existing Wastewater Treatment Plant effluent waters will be blended with the R.O. brine to reduce its salinity in order to meet river discharge requirements.
  • Existing Wastewater Treatment Plant Effluent Pipeline and Delta Diablo Sanitation District Outfall will be used to convey the mixed effluent and brine water to the San Joaquin River for discharge.

Customers, Businesses and Visitors

Construction will have minimal to no impact on vehicle traffic. We welcome the opportunity to address any questions or concerns and encourage interested parties to contact us via the link below with any questions, comments or concerns.

Water treated at the City of Antioch’s Brackish Water Desalination Facility will enter the City’s drinking water distribution system and benefit all residents, businesses and visitors who receive water from the City of Antioch, approximately 112,000 people.  Construction will have minimal to no impact on vehicle traffic.  We welcome the opportunity to address any questions or concerns and encourage interested parties to contact us via the link below with any questions, comments or concerns.


The Project facilities will predominately be located in the City of Antioch, California. The desalination facility will be located within the fence line of the City’s existing water treatment plant at 401 Putnam Street, Antioch and the pipeline routes will follow road right-of-ways. The brine will be conveyed to the Delta Diablo Wastewater Treatment Plant in Pittsburg, CA and then discharged to the San Joaquin River west of the Dow Wetlands Preserve using the existing WWTP outfall.

Project Cost and Financing

The total capital cost of the Project is approximately $110 million which will be financed through a variety of sources. Potential sources include the Department of Water Resources Proposition 1 Desalination Grant, a State Revolving Fund loan, and the City of Antioch’s Water Enterprise Fund.

Project Timeline

Project and Related Documents

December 18, 2020

October 27, 2020

August 11, 2020

July 28, 2020

October 22, 2019

March 6, 2019

October 23, 2018

October 9, 2018

August 14, 2018

August 1, 2018

July 24, 2018

June 26, 2018

December 12, 2017

September 5, 2017

August 8, 2017

July 25, 2017

April 12, 2016

January 26, 2016

Contact Us

If you have any questions or comments, please contact: