Seawater Desalination

The Water Authority is incorporating seawater desalination into its diversified water supply portfolio. This new, drought-proof supply will reduce the region’s dependence on water from the Colorado River and the Bay-Delta that is vulnerable to droughts, natural disasters and regulatory restrictions.

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

Desalination facilities are already treating brackish groundwater from underground aquifers in San Diego County using the same reverse osmosis technology. The Water Authority expects to add desalinated seawater to its supply portfolio with the completion of the Carlsbad Desalination Project by fall 2015.

Seawater Desalination Process

Carlsbad Desalination Project

The first seawater desalination facility in San Diego County – the largest in the Western Hemisphere – is under construction adjacent to the Encina Power Station in Carlsbad.

In November 2012, the San Diego County 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 from the future plant.  This is enough water to meet about 7 percent of the San Diego region’s water demand in 2020.

  Carlsbad Desalination Project under construction adjacent to the Encina Power Station in Carlsbad.

Poseidon Water is a private, investor-owned company that develops water and wastewater infrastructure. It will own and operate the desalination plant In Carlsbad. Poseidon is also building a conveyance pipeline to deliver desalinated seawater to the Water Authority’s aqueduct system. The new 10-mile-long pipeline will be owned and operated by Water Authority.

Water Purchase Agreement

The 30-year 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. It also transfers risks associated with the design and construction of the pipeline to deliver the desalinated water to the Water Authority’s Second Aqueduct in San Marcos.

The Water Authority will purchase water from the plant at a pre-defined price. 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.

Blending seawater desalination with existing supplies

The Water Authority has enhanced its regional water delivery and treatment system to integrate desalinated water. In the city of San Marcos, pipeline facilities are in construction that will connect the new conveyance pipeline to the Water Authority’s Second Aqueduct and control the flow of desalinated water north to the Water Authority’s Twin Oaks Valley Water Treatment Plant. An existing pipeline has been upgraded with a new steel liner to withstand pressurized flows north from San Marcos to Twin Oaks. Improvements at the Twin Oaks Valley Water Treatment Plant allow desalinated water to be stored and blended with imported water that has been treated at the plant. From this location, the blended water can be delivered throughout the region.

The cost of these improvements is incorporated in the total cost per acre foot of desalinated water.

Costs

The agreement sets the purchase price at $1,849 -  $2,064 per acre-foot in 2012 dollars, depending on how much desalinated water is purchased annually. The additional costs for improvements to the Water Authority’s system to integrate the new supply bring the total cost of desalinated seawater to $2,014 -- $2,257 per acre-foot in 2012 dollars, again depending on how much desalinated water is purchased each year. A typical household of four people can expect to pay approximately $5 to $7 more per month when the plant begins producing water by fall 2015.

The Water Authority teamed with Poseidon to secure financing for the desalination plant and the pipeline via tax-exempt construction bonds. Financing closed in December 2012 at a favorable interest rate, bringing financing costs $200 million below the Water Authority’s projections.

When the facility begins producing water, this new supply and its cost will be melded with other water supplies the Water Authority purchases for its 24 member water agencies serving 3.1 million people.

Other Resources

Water Purchase Agreement

Carlsbad Desalination Project Fact Sheet

News Releases

Presentations

Reports

Desalinated Water Conveyance Facilities Alignment Investigation Report (152 mb)

Camp Pendleton Desalination Project

The Camp Pendleton Desalination Project is currently in the planning phase and is being led by the Water Authority, with participation from U.S. Marine Corps Base Camp Pendleton. Early feasibility studies suggest potential for a seawater desalination plant that could produce 100 – 150 million gallons per day. The Water Authority intends to conduct further technical studies at the proposed facility site.

Camp Pendleton Seawater Desalination Feasibility Study Executive Summary Report

Camp Pendleton Seawater Desalination Feasibility Study Final Report – Volume 1

Camp Pendleton Seawater Desalination Feasibility Study Final Report – Volume 2  

Binational Desalination Studies

The Water Authority is participating in a binational feasibility study of a large-scale seawater desalination plant that would be constructed in Rosarito Beach in Baja California, Mexico.  The objective of this study is to evaluate the potential for constructing a seawater desalination plant with a capacity of up to 75 million gallons per day. The water supply from this project could be made available to U.S. and Mexican water users, augmenting Colorado River supplies. Funding for the first phase of this project was shared among the Water Authority, Metropolitan Water District, Central Arizona Water Conservation District, and Southern Nevada Water Authority.  The study is comprised of four phases, the first of which was completed in May 2010.