Frequently Asked Questions

What is seawater desalination?

Desalination is the process of removing salt and other minerals from seawater, brackish water, wastewater, or contaminated groundwater to create pure water for drinking and other purposes. While desalination technologies vary, most modern plants use reverse osmosis, in which high volumes of saline water pass through membranes under high pressure to remove salts.

Desalination is widely considered a water supply option of last resort because of its high cost and extreme energy demands. Seawater desalination plants pose serious threats to marine resources. Giant intake pipes suck up tons of fish and plankton, and the toxic brine left over after fresh water is extracted pollutes coastal waters.

Desalination should be used as an option of last resort. … desalination should only be considered after a region has been successful with conservation and has embarked on substantial water reclamation projects as well. 

New Sources for California's Water Supply

California Assembly Select Committee on Water Consumption and Alternative Sources

Where is it used?

Israel and Australia have both adopted seawater desalination, after exhausting the potential of conservation, efficiency and recycling. Households in Israel and Australia use an average of 44 and 54 gallons per person per day, respectively, while California households use more than twice as much, at 115 gallons per person per day. Israel reuses 94% of its wastewater, compared to 13% in California. Israeli farmers apply an average of 1.6 acre-feet of water per acre of land, while California farmers apply nearly twice as much.

During a severe multi-year drought, Australia spent $10 billion dollars to build six desalination plants. It has now closed four of them, because the water the plants produce is far too expensive compared to other options.

What are the alternatives?

Fortunately, we are living in a time of tremendous innovation, with several water supply options that are more cost-effective and energy efficient than seawater desalination. The most affordable alternative is conservation and efficiency, and California just adopted a new state framework to eliminate water waste and boost both indoor and outdoor efficiency, building on the tremendous water savings that communities achieved during the drought. Recent research from the Pacific Institute, Natural Resources Defense Council, and UC Santa Barbara found that widely-available water conservation and efficiency measures could reduce annual water use in urban areas by up to 57%.

Two other water sources that California is just beginning to tap are stormwater capture and recycling. Stormwater capture costs about one-fourth as much as seawater desalination, and studies indicate that harvesting runoff in urbanized areas of Southern California and the San Francisco Bay Area could provide enough water for about two million people while reducing flooding and water pollution. Water recycling is also more affordable than desalination, and could provide enough water for four million people.

We are seeing these smart solutions adopted all over California, from Orange County’s cutting edge water recycling center – that produces twice as much as the proposed seawater desalination plant for a fraction of the cost – to parks in Los Angeles that harness rain to replenish aquifers.

How would increased seawater desalination impact freshwater systems?

Seawater desalination will not relieve stress on rivers and streams, or on the Bay Delta. Experts from Stanford’s Water in the West explain here. The one exception they identified is the California American Water plant near Monterey, which will reduce surface water withdrawals from the Carmel River because of a state mandate.

We are seeing these smart solutions adopted all over California, from Orange County’s cutting edge water recycling center – that produces twice as much as the proposed seawater desalination plant for a fraction of the cost – to parks in Los Angeles that harness rain to replenish aquifers.

Ocean desalination will not, in the foreseeable future, significantly reduce stress on freshwater resources—particularly freshwater ecosystems. Even the highest production of potable water from ocean desalination in California will not meaningfully reduce stress on freshwater systems, such as the Bay Delta system.

Marine and Coastal Impacts of Ocean Desalination in California

Stanford's Water in the West, Center for Ocean Solutions, Monterey Bay Aquarium, and The Nature Conservancy

What is the future of desalination in California?

Desalination will likely play a limited role in California’s future water supply. In places like Carmel that have exhausted conservation and recycling potential, desalination can be a valuable new water source. For most of the state, however, there are better options to meet water needs. Conservation and efficiency are the easiest and most cost-effective supply options, and the state has a new framework to scale up efficiency.  Recycling and stormwater capture are also more affordable, and are being adopted by communities across the state. These solutions offer an added benefit of reducing polluted runoff, while seawater desalination hurts water quality through the release of toxic brine. California has common sense rules to ensure desalination plants are built in a way that minimizes environmental impacts, but the proposed Huntington Beach plant does not meet these smart standards.  Poseidon wants to use outdated and environmentally damaging 1960’s technology.

Key desal facts


of wastewater is reused in California


potential urban water savings if cities adopt common conservation and efficiency measures