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 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 in late fall 2015.

Seawater Desalination Process

Carlsbad Desalination Project

The first seawater desalination facility in San Diego County – the largest in the Nation – 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 8 percent of the San Diego region’s projected water demand in 2020.

  The Carlsbad Desalination Project (adjacent to the Encina Power
Station in Carlsbad) will be completed in late fall 2015.

Poseidon Water is a private, investor-owned company that develops water and wastewater infrastructure. It will own 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 desalinated seawater with existing supplies

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

Costs

The agreement sets the purchase price at $1,849 to $2,064 per acre-foot in 2012 dollars, depending on how much desalinated water the Water Authority purchases 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 to $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 more per month when the plant begins producing water in late 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 3.2 million people.

Other Resources

Carlsbad Desalination Project Fact Sheet

News Releases

Take a tour of the Carlsbad Desalination Plant

Water Purchase Agreement Documents

For more information on the Water Furnishing Revenue Bonds, Series 2012 (San Diego County Water Authority Desalination Project Pipeline) (Series 2012 Pipeline Bonds), including CUSIPs and the Limited Offering Memorandum, please click here. 

Water Purchase Agreement (Technical appendices to the agreement are available on request)

Board memo and resolution: Potential Adoption of Seawater Desalination Water Purchase Agreement

Environmental Documents for the Carlsbad Desalination Project: 

2006 Final EIR and 2009 First Addenda

2012 Second Addendum

2012 Second Addendum MMRP

Approved Permits and Plans

Reports

Desalinated Water Conveyance Facilities Alignment Investigation Report (152 mb)

Camp Pendleton Desalination Project

A potential Camp Pendleton Desalination Project is currently being evaluated by the Water Authority in collaboration with the U.S. Marine Corps Base Camp Pendleton. Early feasibility studies suggest potential for a seawater desalination plant that could produce 100 million to 150 million gallons per day. The Water Authority is conducting additional technical studies.

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