Frequently Asked Questions Fact Sheet

Water from the West

For more than 50 years, large-scale seawater desalination was just a dream in San Diego County. Today, the region is the hub of the nation’s growing desalination industry and home to the nation’s largest seawater desalination project – all part of an innovative plan to ensure water supply reliability for this semiarid corner of the Southwest.

The Carlsbad Desalination Project will not only improve long-term water supply reliability for the San Diego region, but it also helps all of California by taking pressure off strained water resources during a historic statewide drought.

Decades in the making

desal_benefits1Reverse osmosis – the technology used to remove salt from seawater at the Claude “Bud” Lewis Carlsbad Desalination Plant – was pioneered locally by General Atomics in the 1960s, but it took decades to take hold in San Diego County for a variety of reasons. Even after the statewide drought of 1987-92 spurred interest in desalination, seawater reverse osmosis remained too expensive compared to the region’s historical supplies from the Colorado River and the Sierra Nevada.

The need for long-term, drought-proof water supplies kept rekindling interest in desalination. In 2001, the Water Authority’s Board of Directors approved a Desalination Action Plan. That was followed by studies at potential sites for desalination facilities, including Carlsbad, and by the Board setting a goal to develop 56,000 acre-feet per year capacity for seawater desalination by 2020. At the time, Poseidon Water had locked up a long-term lease at the Encina Power Station site, and the City of Carlsbad invited the Water Authority to take the lead in negotiations with Poseidon.

It took nearly a decade for Poseidon to acquire all the environmental permits that would pave the way for a successful project. Meanwhile, more efficient technologies, rising imported water costs, and growing statewide water reliability concerns improved the feasibility and value of desalination. In 2010, the Water Authority entered into formal negotiations with Poseidon for water supplies. Over the next two years, the parties developed commercial and financial terms for the purchase of desalinated ocean water produced at the Carlsbad plant and delivered to the Water Authority’s regional aqueduct system.

A public opinion survey in 2012 showed strong regional support for desalination, with 82 percent of respondents saying it is important for the reliability of the water supply. In November of that year, the Water Authority’s Board approved a contract with Poseidon that set the terms of the deal. The Water Purchase Agreement helped ensure the project would be built to the highest quality standards while protecting ratepayers by transferring risks associated with building and operating the project to the private sector. It also established that the price of water from Poseidon can only be increased based on predetermined escalation factors, which are dependent on inflation, with the exception of electricity costs. These costs are based on the actual cost of power.

A core, long-term water supply for the region

desal_benefits2The Carlsbad plant uses reverse osmosis membrane technology to produce enough water to meet approximately 10 percent of the region’s water needs as a core supply of water regardless of weather conditions. The desalination project includes three main components: the desalination plant adjacent to the Encina Power Station on Agua Hedionda Lagoon; a 10-mile pipeline that connects to the Water Authority’s regional distribution system; and upgrades to Water Authority facilities for distributing desalinated seawater throughout the region. In a typical year, the plant will generate about one-third of the San Diego region’s locally produced water supplies, providing a highly reliable water supply designed with state-of-the-art technology to reduce energy demands.

After 30 years of operation at the Carlsbad plant, the Water Authority has the option – but not the obligation – to purchase the plant for $1. The agency also has the right to buy the facility after 10 years, though it isn’t required to do so.

Frequently Asked Questions


Water from the desalination project is blended with imported water supplies at the Water Authority’s Twin Oaks Valley Water Treatment Plant north of San Marcos for distribution around the region. Some parts of North County don’t directly receive desalinated seawater; however, they still benefit from the use of desalination to meet the regional demands.

The taste of tap water commonly varies based on the blending of supplies from different sources, such as the Colorado River and the Bay-Delta. Adding desalinated seawater to the mix may also slightly alter the taste. The water meets or exceeds all federal and state drinking water standards.

Water from the plant will add about $5 to the typical homeowner’s monthly water bill, at the low end of projections when the project was launched in late 2012.

It took about three years for the project to be completed after ground was broken in December 2012.

The Carlsbad Desalination Project is part of the Water Authority’s long-term strategy to improve water supply reliability to enhance the quality of life for the region’s 3.3 million residents and support the region’s $222 billion economy. As one piece of the region’s diversified water supply portfolio, the plant provides a locally controlled, drought-proof source of supply that isn’t subject to the same uncertainties as imported supplies from the State Water Project.

The Water Authority’s Board of Directors in September 2015 approved a new agreement with U.S. Marine Corps Base Camp Pendleton to study seawater intake options for a potential seawater desalination project on base. The Board also authorized a $4.05 million contract for building, operating and reporting on a pilot- scale seawater intake testing program that’s expected to take about two years. Future decisions regarding whether to proceed with a full-scale project will take into account current water demands, progress with the implementation of other local water supplies, progress on upgrades to the Sacramento-San Joaquin Bay-Delta, and changes in imported water supply reliability.

No. Water from the plant is part of the region’s core supply. If demand levels fluctuate downward during a wet year, the Water Authority might purchase fewer supplies from the Metropolitan Water District of Southern California, depending on the region’s water needs.