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.
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.
In 2019, ownership of the plant was purchased by Aberdeen – a global infrastructure investment firm. Aberdeen established Channelside Water Resources, which now manages the daily operations of the desalination plant. All provisions of the Water Purchase Agreement are still in place.
Key Documents
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.
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.
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Desalination 101 (The nuts and bolts)
The Claude “Bud” Lewis Carlsbad Desalination Plant is capable of delivering more than 50 million gallons of fresh, desalinated drinking water per day – enough to serve approximately 400,000 people in San Diego County. Commercial operations began in late 2015, providing the region with a reliable and locally controlled water source.
The Desalination Plant and Process Locations
Drawing Water from the Pacific Ocean
On a typical day, the Carlsbad plant uses 100 million gallons of seawater from the Pacific Ocean that enters through an intake on the shores of Agua Hedionda Lagoon. Seawater is drawn into the pump station and transported to the plant via the 72-inch seawater feed pipe to begin the desalination process.
Roughly half of the water flowing through the plant is converted into drinking water for the region. The remaining water, carrying all of the original salt and minerals, is returned to the ocean through the lagoon.
Removing Impurities
Most people think of desalination only as removing salt, but the process also removes other mineral, biological and organic impurities to produce extremely high-quality water.
When seawater arrives at the plant, it goes through a pretreatment process to eliminate algae, organic materials and other particles. Seawater is pumped into multimedia filter tanks which contain layers of anthracite and sand atop a bed of gravel. Then, the water moves into the second pretreatment stage to remove smaller impurities.
Secondary Pretreatment
Before seawater enters the reverse osmosis filters to separate the salts, it must go through the second stage of pretreatment called microfiltration to remove smaller – oftentimes microscopic – impurities. At this point, virtually all impurities other than dissolved salts and minerals have been removed from the water, but it still needs to go through one more step to remove the dissolved salts and minerals to be ready for drinking.
The Center of the Desalination Process
Reverse osmosis is the heart of the Carlsbad plant. During this process, dissolved salt and other minerals are separated from the water, making it fit for consumption. This reverse osmosis building contains more than 2,000 pressure vessels housing more than 16,000 reverse osmosis membranes.
Returning Salty Water to the Sea
The byproduct of reverse osmosis – called brine – contains roughly twice as much salt as seawater. Before it’s discharged to the ocean, brine from the plant is diluted with seawater to reduce its salinity and ensure minimal impacts to the ocean.
Recycling Energy to Conserve Resources
The Carlsbad plant uses energy recovery devices that recycle the pressure from the reverse osmosis process. These devices save an estimated 146 million kilowatt-hours of energy per year, reducing carbon emissions by 42,000 metric tons annually – roughly equivalent to the annual greenhouse gas emissions from 9,000 passenger vehicles.
There are 144 energy recovery devices at work in the plant, reducing the overall energy consumption of the reverse osmosis process by 46 percent.
The energy recovery devices capture the hydraulic energy created by the high pressure reject stream of seawater produced during the reverse osmosis processes and transfer it into incoming seawater, without consuming any electrical power themselves.
Finishing the Process
After reverse osmosis filtration, the fresh water is nearly ready for consumption. But before making its way into your faucet, the water must undergo “post treatment.” This includes adding some minerals back into the water and disinfection with chlorine.
From the Carlsbad Desalination Plant to You
Now the water begins its journey from the plant to taps all across San Diego County. That process starts by pumping water through a 10-mile, 54-inch pipeline to the east through Carlsbad, Vista and San Marcos to the San Diego County Water Authority’s Second Aqueduct. Then, the water moves north to the Water Authority’s Twin Oaks Valley Water Treatment Plant, where it’s blended with imported water supplies and routed into large-diameter pipes for delivery throughout the region.
The Carlsbad Desalination Project meets rigorous environmental standards set by state and local agencies, including the California Coastal Commission. By boosting the project’s energy efficiency, offsetting greenhouse gas emissions and enhancing coastal habitat, the project was designed with environmental stewardship in mind.
The Channelside Water Resources Climate Action Plan calls for the plant to be net carbon neutral over 30 years by offsetting greenhouse gas emissions from project operations. This is done through the purchase of carbon offsets and energy recovery technology at the desalination plant.
Energy recovery devices save an estimated 116 million kilowatt-hours of energy per year, reducing CO2 emissions by 42,000 metric tons annually – roughly equivalent to the annual greenhouse gas emissions from 9,000 passenger vehicles.
The Channelside Water Resources is also restoring approximately 125 acres of wetlands in San Diego Bay and the Channelside Water Resources is preserving the 400-acre Agua Hedionda Lagoon by assuming responsibility for the continued stewardship of the lagoon.
The cost of water
Water from the Carlsbad Desalination 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.
Desalinated water from the plant costs typical homeowners about $5 per month, at the low end of projections when the project was launched in late 2012.
Based on current electricity cost estimates, the Water Purchase Agreement sets the price of water from the Carlsbad Desalination Plant depending on how much is purchased annually. The first 48,000 acre-feet of water purchased each year will pay for the fixed costs of the project and the variable costs of water production. The Water Authority has the option to purchase an additional 8,000 acre-feet per year at a lower rate that reflects only the variable costs of incremental water production.
In December 2012, financing for the Carlsbad Desalination Project closed successfully, bringing with it $734 million in tax-exempt bond financing. The Water Authority worked with the Channelside Water Resources to secure a favorable interest rate of 4.78 percent, saving an estimated $200 million in financing costs over three decades compared to earlier projections. Independent analysts cited the Water Authority’s financial stability and strong credit ratings, along with the strategic importance of the desalination plant, as critical factors in their positive assessments of the debt.
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, 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