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Carlsbad Desalination plant Carlsbad Desalination plant Carlsbad Desalination plant

The Western Hemisphere’s
biggest seawater desalination plant

The Carlsbad plant was designed to fit on a site less than 30% as large as typically required.

Carlsbad Desalination plant Carlsbad Desalination plant Carlsbad Desalination plant


San Diego County has limited local water resources, with relatively small aquifers and no major rivers. In recent decades, the county has imported more than 80% of its water from Northern California and the Colorado River.

Developed by Poseidon Water under a 30-year Water Purchase Agreement with the San Diego County Water Authority, the Carlsbad Desalination Project is an important part of the Authority’s long-term strategy to improve the reliability of the region’s water supply.


Mott MacDonald provided technical advisory services to Stonepeak Infrastructure Partners, the private equity investor for the project, from the project initiation to plant commissioning and testing.

The project was designed and built on a site of under six acres (2.4 hectares): less than 30% the size typically required for a facility of this type. This site optimization allowed the project to be built within the existing Encina Power Station site and to avoid the additional costs of land acquisition and corresponding environmental impacts.


When it opened in December 2015, the Carlsbad Desalination Plant was the largest seawater desalination plant in the Western Hemisphere, with a capacity of 189,000 cubic meters per day.

The $1 billion project, which included the desalination plant and a 10-mile (16-kilometer) pipeline, required 1.5 million hours of work in Carlsbad, and supported an estimated 2,500 jobs and infusion of $350 million into the local economy. The project was completed on schedule and on budget.

With state-of-the-art energy recovery devices, this was the first major desalination plant in California to have a small carbon footprint. In addition to providing a reliable year-round source of high quality drinking water, the management of the plant ensures the continued stewardship of the 300-acre (121-hectare) Agua Hedionda Lagoon.

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