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There are numerous proposals to build desalination facilities along California's coast. Desalination facilities have also been proposed in several other states including Texas and Hawaii and a facility has been built in Tampa, Florida. This discussion and issue summary is for Surfrider Foundation activists and others who wish to become informed regarding desalination and participate in review of a planned desalination plant. We hope this background paper highlights some of the issues of concern when evaluating the prudence of building a desalination facility in your area. Also, we hope this provides a little "food for thought" when considering alternatives to desalination, or alternative technologies and practices for implementing desalination.

Note: This article was originally written in 2003 and has been updated several times since then as additional information regarding the costs and potential environmental impacts of seawater desalination have become available. In May 2014, the Natural Resources Defense Council (NRDC), in collaboration with Surfrider Foundation and several other environmental organizations published an issue brief Proceed With Caution: California's Drought and Seawater Desalination, which covers many of the same issues explored in our article.


Producing drinking water from seawater has been technologically achievable for several decades. Until recently, however, application of seawater desalination ("desal") on a large scale has been primarily limited to arid regions of the world that have a cheap supply of energy, such as in the Middle East. Saudi Arabia produces 30% of the world's output of desalinated seawater. The cost of energy is important due to the fact that the two primary technologies used for desalination, distillation and reverse osmosis, require a lot of energy, either to boil and then re-condense water (distillation) or to force water molecules through semi-permeable membranes at high pressure (reverse osmosis).

The cost estimates for desalination plants in the United States vary based on volume. For instance, the estimated cost per acre-foot of desalinated water for a 50 million gallon per day (MGD) facility in Carlsbad, California was estimated to be between $1,915 and $2,140 per acre-foot. This facility went online in December 2015 and the 2019 SDCWA Annual Report stated that the actual unit cost of Carlsbad Desalination Plant's product water was a whopping $2,685 per acre-foot and is expected to increase 5 percent over the next year, around $2,800 per acre foot.

Desalinating seawater at a nearly identical proposed 50 MGD facility in Huntington Beach, California has been estimated to cost between $1,500 and $2,300 per acre-foot. In southern California, the Metropolitan Water District has offered local water agencies subsidies of up to $250 per acre-foot to implement desalination projects. This subsidy reduces the cost of producing desalinated drinking water and makes desalination facilities more economically viable for local water agencies. However, the subsidies only defray costs and do not reduce the cumulative costs in the region. Furthermore, many of these subsidies are not intended for research and development, and consequently will not directly lower the overall cost of producing freshwater through desalination over time. A paper by David Zetland published in 2014 examines three cases where the costs of desal have been obscured by various methods.

A desal facility using reverse osmosis technology forces seawater through membranes with tiny pores large enough to pass water molecules but too small for salt molecules. For every two gallons of seawater introduced, about one gallon of drinking water is produced and one gallon of concentrated brine (about twice the normal salt concentration of seawater) is returned to the ocean.

Several seawater desal facilities have recently been proposed in California, Hawaii and Texas and a large facility has been constructed to produce 25 MGD of drinking water in Tampa, Florida. The Florida project has experienced technical difficulties that impaired full production and have clouded the economic and environmental post-operation analysis. In California, a State Desalination Task Force has reviewed desalination and has created draft issue papers and a final report (2003).

The California Coastal Commission has also prepared a report on desalination and associated California Coastal Act applicability (2004).

Simultaneously, several California state and local government agencies are currently grappling with the numerous regulatory issues confronting permit applications for coastal desalination facilities. Some of these same agencies also have regulatory authority and/or budgetary discretion over implementing alternative technologies and rules to provide additional water -- primarily through wastewater reclamation and/or conservation.

The stated benefit of desal is primarily to provide a reliable new source of freshwater to supplement finite (or dwindling) existing sources that can not meet projected water demand. Desalination may also include the environmental benefit of reducing our unsustainable reliance and over-drafting of rivers, streams and aquifers, thereby reducing the adverse environmental impacts on those resources. Also, a constant flow of freshwater from desalination could avoid the environmental disruption of building more dams for storage. However, to ensure that these potential environmental benefits come to fruition could require complex legal mechanisms and each project proposal might involve different complications.

Desal facilities can have several potential negative environmental impacts, depending upon where they are located, how they are designed and operated, and the end use of the produced water. In some cases, there are also concerns about "privatizing" what has always been a public resource, as well as additional complications if a private owner is a foreign entity. See the video below to hear some of the serious issues that one coastal community is concerned about when it comes to a private company attempting to build a large desalination facility:

Listed below are some of the potential negative impacts of desal projects:

Issue Summary

1. Seawater Intake. There are several alternatives for gathering the "source" water for desalination: intake pipes in the ocean, beach wells (seawater aquifers) and intake galleries (collection systems buried beneath nearshore sediment). Unless the seawater intake is gathered from beach wells or galleries there is an inevitable destruction of marine life (fish and smaller marine life like eggs and larvae) as the water is drawn into the desal plant. "Impingement" is the term for the mortality of larger animals that are trapped and killed on the intake screens, and "entrainment" refers to smaller organisms (e.g., larvae and eggs) that slip through the screens and are killed once they enter either the reverse osmosis membranes of the desal plant or the cooling condensers of an adjacent electric generating plant.

One of the reasons that desal plants are often proposed for co-location with coastal electric generating plants is that they take advantage of the existing cooling water intake and outfall pipes. Desal "source" or "feed" water is typically taken off of the discharge (hot) side of the power plant cooling water system and the concentrated brine is discharged by mixing it with the remaining cooling water return to the ocean. In this way, no additional seawater is drawn from the ocean, and proponents argue that no "additional" marine life mortality is attributed to the desal process. However, although there is some debate about the degree to which sea life survives the trip through a power plant cooling system, any sea life that did survive would then be destroyed by the filtration and reverse osmosis steps of the desal process. Furthermore, because of the energy-intensive nature of desalination plants, co-location of these plants could mean that the generator is in use when it otherwise wouldn't be. The more the generator runs, the more water it takes for cooling, the more fish that die. The cumulative energy demands of desalination facilities will translate into additional electric generator output to supply the desal facilities.

The US Environmental Protection Agency, under a court order, is currently reviewing the rules on cooling water intakes for power plants. Cooling water intakes are regulated under the authority of the Clean Water Act Section 316 (b), and the EPA is reviewing whether "once-through" cooling (OTC) meets the "best technology available" standards mandated by that Act. Generators could be compelled, at least in many circumstances, to retrofit the plant with cooling towers that recycle water. These towers cool the water with forced air from large fans. This technology would either eliminate or dramatically reduce the marine life mortality and cumulative impacts on marine ecosystems from once-through cooling. In California, the OTC Policy Adoption and Approval Process is nearing completion. On May 4, 2010 the State Water Board adopted the Policy on the Use of Coastal and Estuarine Waters for Power Plant Cooling to establish technology-based standards which implement federal Clean Water Act section 316(b) and reduce the harmful effects associated with cooling water intake structures on marine and estuarine life. This policy was amended in 2011.

As of 2020, Ten plants have ceased their once-through cooling operations. Eight of the remaining plants have informed the State Water Board that they are planning to comply by retiring their existing OTC plants’ equipment. In some cases, plants will repower their locations with modern non-water-cooled systems. Dynegy’s Moss Landing Power Plant is the only OTC plant that is complying with the OTC Policy through Track 2. However, the State Water Resources Control Board is currently considering a draft OTC Policy amendment for Extension of Compliance Schedules of Alamitos, Huntington Beach, Ormond Beach, and Redondo Beach Generating Stations. The State Water Board is proposing to extend the policy for these plants for three years until December 31, 2023, and Redondo Beach Generating Station for one year through December 31, 2021, to address system-wide grid reliability concerns. Additionally, the proposed amendment amends the compliance date for Diablo Canyon Nuclear Power Plant Units 1 and 2 by reducing Unit 1 by two months and extending Unit 2 by 8 months to November 2, 2024, and August 26, 2025, respectively to match the expiration date of each unit’s Nuclear Regulatory Commission license.

Furthermore, under the "consistency" authority granted the states through their participation and compliance with the federal Coastal Zone Management Act, coastal states may review permits granted by federal agencies. The state agency in charge of the coastal zone management plan can then deny the federal permit if it is found to be inconsistent with the state's management plan. This means that the coastal management authority could either deny the cooling water intake and/or discharge permits for a co-located coastal power plant and/or desalination facility.

For more on this issue, see Key Issues in Seawater Desalination in California - Marine Impacts (Pacific Institute, 2013).

2. Estuaries vs. Ocean Source Water. There has been a dramatic loss of estuarine habitat in California, ­especially in the southern region of the state. Most of our coastal wetlands and estuaries have been filled and developed or are highly degraded from pollution and unnatural sediment loading. Consequently, estuarine habitat is a precious commodity and this creates heightened threats to aquatic and terrestrial life that depend on estuaries for some stage of their life history (e.g., birds, fish, invertebrates, etc).

Therefore, desalination facilities that rely on estuarine "source" water should be viewed with heightened scrutiny. Many of the entrainment and impingement issues that impact marine life and healthy marine ecosystems are arguably made worse when they impact estuarine species and the intricate ecological balance of estuarine ecosystems.

3. Brine Discharge. Seawater contains about 35,000 parts per million (ppm) salt. During the reverse osmosis process, water molecules are forced through membranes while the salt particles are retained by the membrane and end up in a "reject stream" that is about twice as salty (70,000 ppm) as seawater. If this were discharged directly back into the ocean or into a coastal estuary there would likely be some negative impacts to sea life in that immediate area of the discharge. If a desal plant is located next to a power plant, they can mix this brine water with the higher volumes of "hot" cooling water that are being returned to the ocean. This dilutes the brine and marginally lowers the discharge temperature so there is arguably less of an impact on sea life. In the same vein, desalination plants might be co-located with wastewater treatment facilities, or connected by pipes, so the brine could be mixed with the freshwater discharge and possibly reach a salt concentration and temperature closer to ambient ocean conditions.

The impacts on marine life are, for the most part, dislocation of indigenous populations. For instance, the marine life normally found in the area of the discharge (the Zone of Initial Dilution ­ or ZID) might be displaced and the area re-inhabited by organisms more tolerant to dynamic salt concentrations and temperatures (e.g., estuarine species). Furthermore, the concentration of dead marine life in the discharge may attract an uncommon congregation of filter feeders and other scavengers. In short, the natural ecosystem is disrupted, but this does not necessarily lead to lower biomass in the area. However, this would be a site-specific determination and would depend on variables like ocean current, depth, and maybe most importantly, how close the discharge is to sensitive and essential fish habitat.

For more on this issue, see Key Issues in Seawater Desalination in California - Marine Impacts (Pacific Institute, 2013).

4. Building on the Coast. Although desal plants are not nearly as huge or ugly as power plants, they are an industrial facility that some people may object to. Being located along the coast, the structures may impair views, block coastal access, result in the filling of wetlands, or otherwise negatively impact the experience of going to the beach. Additionally, as sea levels rise, desalination plants may be subject to coastal hazards - posing a financial risk and potentially resulting in reliance upon shoreline armoring.

5. Growth Inducement? If the water produced from desal is used to reduce our reliance on imported water and more water then ends up being retained in water source areas to help sustain the environment there, then desal may produce a net environmental benefit. If, on the other hand, the water not taken from these rivers is diverted to other users and the river doesn't benefit, desal may not result in a net environmental benefit. And if the desal plant fuels new growth along the coast rather than just replacing imported water, it may contribute to environmental degradation. This question of whether water is for "replacement" or "new source" is at the heart of the question of "growth inducement."

It is also important to note that many of the current proposed projects are located in areas with dramatic surface run-off problems and limited sewage treatment capacity. Adding a "new" source of freshwater to this system will arguably exacerbate an already difficult problem as the produced water is used and becomes wastewater and urban runoff.

These direct and indirect concerns about growth inducement are difficult, if not impossible, to quantify and analyze without the project proponent identifying the "end user" of the water supply. It is therefore important that any Environmental Impact Report (EIR) or other environmental analysis of the project identify the end user(s). The EIR should also evaluate project alternatives that may have less environmental impact, including water conservation and recycling.

6. Cost and Power Use. Desal is an expensive way to make water and uses a lot of electricity. Water most be pumped through special membranes at about 900 pounds per square inch (psi) pressure to remove the salt, then the water often must often be pumped several miles to a water distribution network. Depending on the specific project proposed, water costs to consumers may go up at least 30% and could more than double. The required electrical energy is often produced by fossil fuel burning power plants that cause air pollution.

In 2016, the Pacific Institute released a report analyzing alternative water supply options – listing desalination by far the most expensive of water supply options. See: The Cost of Alternative Water Supply and Efficiency Options in California. Poseidon’s Carlsbad plant report that in 2018, it was $3 million over budget due to what they called an “unexpected” increase in energy costs. In April 2019, UCLA’s Luskin Center published an Environmental Justice Analysis for Poseidon’s proposed Huntington Beach plant and concluded that the cost of the water would unduly burden the region’s environmental justice communities.

7. Dependence on Power Plants. As mentioned above, there are logical reasons to locate desal facilities next to power plants. But power plants are under pressure to eliminate their use of "once through" cooling water that kills fish. See here and here for more information on this topic. Power plants may be required by the U.S. EPA or state agencies to install a "closed loop" cooling system that reduces the amount of seawater intake and fish kill by 90% or more. Some may convert to an air cooling system that uses no water or a recirculating cooling water system that uses a cooling tower and reduces seawater intake by 90% or more. If these changes take place, it may no longer make sense to locate the desal plant next to the power plant. In fact, it may no longer make sense to locate power plants along the coast. Looking at this another way, if a desal plant is installed at an existing coastal power plant facility, that may not be a good investment if the power plant cooling system that is the basis for the desal plant is removed or modified. From the power company's perspective, if a desal plant is built next to a power plant, that may represent a disincentive to upgrade the power plant's cooling system or to build a more efficient new power plant.

8. Alternative Sources of Potable Water: As with any social choice, the determination to implement desalination facilities should be compared with other alternatives. Some of the possible alternatives include improved water conservation and greater implementation of wastewater reclamation.

Although water agencies are constantly struggling to provide citizens with affordable and reliable drinking water, it is evident that we still do not use water very efficiently. This is directly apparent in the amount of urban runoff that we see every day. There is some concern that desal will reduce the drive to use existing sources of water efficiently, and consequently negatively impact programs to advocate for water conservation. The southern California region has experienced dramatic population growth over the past several years. Yet, the demand for water has remained relatively constant, ­in large part because of efforts at water conservation. These current conservation efforts are arguably only scratching the surface of what could be a much broader effort in the southern California region, and other areas of the country may not be employing these strategies at all.

Water reclamation is the practice of treating wastewater to allow re-use the water. Although there has been considerable controversy surrounding the use of reclaimed water as a source of drinking water, this practice (indirect potable reuse) has been implemented on a large scale. There are also many examples of successful programs that either use this water for irrigation (offsetting the need to use drinking water for this purpose), or for injection into groundwater aquifers (reducing the negative impacts from over-drafting our aquifers and/or reserving this water for potable uses in the future). Besides providing a reasonable alternative to desalination, widespread implementation of reclamation could dramatically reduce the amount of partially treated or untreated wastewater being discharged into the ocean. Just such a system has been in operation in Orange County, California since 2008 and implementation of a similar system is underway in San Diego.

In addition, in many places we have either over-used or polluted our groundwater. On the one hand, if desal should reduce our dependency on groundwater, some of these "over-drafted" groundwater aquifers could be allowed to recover. On the other hand, we may be less inclined to properly manage or clean up our ground water resources. Interestingly, reverse osmosis technology has also been proposed and implemented as a means for cleaning up and using polluted or brackish groundwater.

In conclusion, reviewing alternatives to desal should not only consider the dramatically lower cost of conservation and reclamation, but should also account for the benefits of reducing the pollution reaching our waterways through urban runoff and sewage discharge.

9. Private Ownership: The California Coastal Commission report on desalination raises a number of concerns regarding private ownership of desalination facilities. Historically, the ocean has been regarded as a public resource to be utilized and enjoyed by all people and animals in a sustainable, non-extractive manner. Using the ocean as a source of drinking water (clearly an extractive use) changes all that. While one desal facility may not have a significant effect on the ocean, many such facilities (see cumulative impacts discussion below) may have detrimental effects.

Typically, most of the water supply infrastructure in the United States is owned and operated by public or semi-public agencies. Quality of the water, reliability of the water supply system, and the price of the delivered water are all subject to the scrutiny of various regulatory agencies, local governmental bodies, and the general public. A water supply system operated by a private company (perhaps a multinational company) may not be subject to the same restrictions. Their profit goals may encourage rate increases, reductions in quality, and promotion of more water use, as opposed to calls for more water conservation and recycling.

The subject of ownership by a multinational private company raises additional concerns regarding potential challenges to U.S. laws that a multinational corporation might regard as restrictions on "free trade" or an undue limitation on their ability to make a profit.

10. Cumulative Impacts: An environmental analysis conducted under CEQA (California Environmental Quality Act) or NEPA (National Environmental Policy Act) should include an assessment of the cumulative impacts of not only the proposed project, but also other proposed projects (and existing facilities) in the area. These impacts would include the cumulative entrainment/impingement bioregion impacts, cumulative energy consumption impacts, cumulative growth-related impacts, and cumulative wastewater & urban runoff impacts, among others. This is especially important in areas where existing air quality, water quality or ecosystem health is already compromised. In California, as many as 21 new seawater desalination facilities have been proposed, with a cumulative production capacity of up to 240 million gallons per day. Some facilities are within a few miles of each other, potentially impacting the same bioregion of the ocean and/or other common environmental resources. These projects should not be reviewed in a vacuum.

11. Reliability and Compliance: In 2019, Poseidon’s Carlsbad Plant was unable to deliver 5,071 acre-feet of requested water – raising questions about the reliability of desalination. As such, Poseidon paid the SDCWA $1,965,989 for non-delivery of water. In 2017 and 2018, the plant fell short on water delivery by approximately 20% on average, and in the third quarter of 2017, operating capacity was at just 42%. Is this really the rate of reliability we want to depend on for critical water sources?

In 2019, Poseidon received five notices requesting corrective action associated with permit compliance. For several years, Poseidon’s Carlsbad plant failed approximately 30% of chronic toxicity tests and was unable or unwilling to resolve the issue. A Toxicity Evaluation Report was completed and the results of the cause were inconclusive, citing that likely a confluence of chemical and polymer additives were at fault. Additionally, researchers at UC Santa Cruz collected data that suggests the brine from the Carlsbad plant may be exceeding the brine mixing zone limitations with potential biological implications.

There are ways to make desalination much less impactful and harmful to humans and marine life. One of those is to use subsurface intakes. Surface intakes are a way to reduce marine life entrainment and impingement associated with open ocean seawater intake and also it reduces the toxicity of discharge by avoiding chemical additives in the first place. We must locate desalination plants in places where subsurface is feasible.

One study surveyed sea water reverse osmosis plants located globally and found that "[i]n many cases, the water produced from a subsurface intake can be transmitted directly to the cartridge filters, thereby eliminating mixed media filtration, coagulation processes, and the need to use various chemicals (e.g., ferric chloride, chlorine). Thus, subsurface intakes would clearly reduce the likelihood of toxicity exceedances in brine discharge.


Water conservation and recycling are often better alternatives for balancing water supply and demand than seawater desalination. In almost all cases recycled water can be obtained at a lower cost than desalinated seawater. Treating and recycling wastewater also helps to protect human and ecological health by reducing wastewater discharges to the ocean. A case study example of how to do it right can found in Santa Cruz, California, where local activists successfully waged a multi-year battle to advocate for conservation over desalination.


With the rise of interest in desalination, partly caused by improvements in reverse osmosis technology, there is a wealth of information coming to the forefront. This fast growing interest in desalination has also caused government agencies and non-governmental organizations to quickly begin discussions about policy that will guide the implementation of this technology. We suggest that any review of local proposals include a thorough research of all of the issues outlined above. We have provided a list of reference sites to start your research. Please feel free to contact Mandy Sackett or Katie Day at the Surfrider Foundation National Headquarters if you have questions or recommendations about the discussion surrounding desalination.

New! Desal fact sheet. This fact sheet was prepared in December 2015 in conjunction with the opening of Poseidon's Carlsbad desalination facility. Although it refers to that facility, the document is also applicable to Poseidon's proposed Huntington Beach facility.

More New! In May 2016 a report Marine and Coastal Impacts of Ocean Desalination in California was released. In January 2016, the Stanford Woods Institute for the Environment, through its Water in the West Program and the Center for Ocean Solutions, collaborated with the Nature Conservancy and the Monterey Bay Aquarium to organize and facilitate an “uncommon dialogue” on the coastal and marine impacts of ocean desalination among leading experts from nongovernmental organizations, private industry, government agencies and academia. The dialogue had two primary objectives: 1) to promote information exchange and open discussion regarding the best available science, technology and policy related to marine and coastal impacts of desalination projects in California and beyond; and 2) to identify key issues and knowledge gaps for future research and policy development with respect to marine and coastal impacts of ocean desalination in California. To accomplish these objectives, the dialogue was split into four sessions: (1) Scope of Desalination and Current Regulatory Framework in California, (2) Seawater Intakes, (3) Brine Disposal, and (4) Facility Siting and Community Impacts. This report synthesizes and summarizes the proceedings and conclusions of that dialogue. The overall findings were as follows:

  • While desalination may prove critical for a few coastal communities, it is unlikely to be a major part of California’s water supply portfolio due to its high cost of operation, the availability of other sources of water (such as recycled wastewater), its high energy use and the resulting high levels of greenhouse gas emissions, and siting difficulties given the fragility and importance of California’s coastal ecosystems.
  • Given the relatively small potential footprint of ocean desalination, it is not likely to play a meaningful role in reducing the stress on freshwater ecosystems caused by diversions for water supply.
  • Using an integrated spatial approach to identify marine and coastal areas of high ecological and natural value, as well as areas that have local need and existing beneficial infrastructure, could effectively complement California’s new desalination policies and help guide sustainable desalination development for California.
  • Future work is needed to further define the elements of sustainable desalination projects and develop policies to incentivize adoption of those elements. Elements of sustainable desalination identified at the conference included projects that are smaller; that provide supply to meet a specific, clear local demand; that are located away from sensitive and valuable marine areas; and that are powered by renewable energy sources.
  • California’s new ocean desalination policy has taken important steps to reduce the environmental effects of both ocean water intakes and brine disposal, yet a need remains for further study in minimizing impacts in a site-specific context and in advancing technologies, particular technologies for surveying and monitoring such site-specific impacts. Better evaluation of data from facilities around the world and better monitoring of facilities built in California were both identified as important avenues for research.
  • In making decisions about water supply, water managers may not have access to good information about the true costs of water from different sources, including financial costs, environmental impacts, impacts on the source community (if the water is imported) and potential economic impacts on the state as a whole. A rigorous examination of the full costs, benefits and trade-offs of desalination in the context of the full costs and sustainability of current water supply solutions would improve decisions about desalination and water supply more generally and the public’s understanding of the trade-offs involved in those decisions.

References and Additional Information Resources

This article is part of a series on Clean Water which looks at various threats to the water quality of our oceans, and the negative impacts polluted waters can have on the environment and human health.

For information about laws, policies, programs and conditions impacting water quality in a specific state, please visit Surfrider's State of the Beach report to find the State Report for that state, and click on the "Water Quality" indicator link.