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Leading the Nation in Seawater Desalination

The Water Authority added desalinated seawater to its supply portfolio in 2015 with the start of commercial operations at the nation’s largest seawater desalination plant – the result of a public-private partnership in the coastal town of Carlsbad. This new, drought-proof supply reduces the region’s dependence on supplies that are vulnerable to droughts, natural disasters and regulatory restrictions.

What Is Desalination?

Desalination uses reverse osmosis technology to separate water molecules from seawater. Water from the ocean is forced through thousands of tightly-wrapped, semipermeable membranes under very high pressure. The membranes allow the smaller water molecules to pass through, leaving salt and other impurities behind.

infographic outlining the 3 steps of desalination.  This information is also summarized in the paragraph abo e this image.
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Carlsbad Plant

A landmark public-private partnership

In November 2012, the Water Authority approved a 30-year Water Purchase Agreement with Poseidon Water for the purchase of up to 56,000 acre-feet of desalinated seawater per year, approximately 10 percent of the San Diego region’s water demand.

Poseidon is a private, investor-owned company that develops water and wastewater infrastructure. Under the Water Purchase Agreement, Poseidon built the Claude “Bud” Lewis Carlsbad Desalination Plant, and a 10-mile conveyance pipeline to deliver desalinated seawater to the Water Authority’s aqueduct system.

The Water Purchase Agreement assigns appropriate risks to the private sector while keeping costs for water rate payers as low as possible. The agreement transfers to Poseidon and its investors the risks associated with design, construction and operation of the desalination plant.

The Water Authority purchases water from the plant at pre-defined prices. If the water does not meet quality requirements specified in the agreement, the Water Authority does not pay. The agreement also specifies that the Water Authority has the right to ensure that the plant is operated and maintained in a safe, efficient manner consistent with industry standards. At the end of the agreement’s 30-year term, the Water Authority may purchase the plant for $1.

drinking water stoarge tanks at desalination plant

About the plant

The plant provides enough high-quality water to serve about 400,000 people. It is part of a $1 billion project that includes the nation’s most technologically advanced and energy-efficient seawater desalination plant, a 10-mile large-diameter pipeline and improvements to Water Authority facilities for distributing desalinated seawater throughout San Diego County.

Water from the Carlsbad plant is more expensive than the region’s traditional imported water sources, but it has the significant advantages of being drought-proof and locally controlled. The plant also is south of the major Southern California fault lines, providing added water supply security in case an earthquake severs imported water supply lines.