The United States operates roughly 1,500 desalination facilities, though the exact count shifts depending on how you define “plant” and which database you consult. Many of these are modest brackish-water treatment systems serving small communities or industrial users, not the massive seawater facilities that tend to dominate headlines. The distinction between brackish and seawater desalination matters more than most people realize, because it shapes everything from cost and energy use to where plants can be built in the first place.
Why the Count Is Hard to Pin Down
Desalination in the US spans an enormous range of scales and technologies. A small municipal well-water system that strips dissolved minerals from slightly salty groundwater technically qualifies as a desalination plant, as does a billion-dollar coastal facility that pulls drinking water from the Pacific Ocean. Some inventories count every membrane unit that reduces salinity, including those embedded inside larger water treatment works. Others count only standalone facilities designed primarily for desalination. The result is that different agencies and industry groups report different totals.
What is consistent across sources is that the overwhelming majority of US desalination capacity treats brackish water, not seawater. Brackish water sits somewhere between fresh and fully saline, and it requires considerably less pressure and energy to desalinate. Only a handful of large seawater reverse osmosis plants operate on US coasts, while hundreds of smaller brackish plants dot inland states and coastal aquifer zones. Florida and Texas together account for a disproportionate share of the nation’s total desalination capacity, with California home to the most prominent seawater facility.
Where US Desalination Plants Are Concentrated
Geography drives desalination in the US more than any single policy or technology trend. States with limited freshwater supplies, growing populations, or naturally brackish groundwater are the ones that have invested most heavily.
- Florida: Leads the country in total number of desalination plants, most of them treating brackish groundwater. The Tampa Bay Seawater Desalination Plant, which came online in 2007, was one of the first large seawater facilities in the country and can produce around 25 million gallons per day.
- Texas: Has dozens of brackish groundwater desalination facilities, particularly in the western part of the state where freshwater sources are scarce. El Paso’s Kay Bailey Hutchison plant is one of the largest inland desalination plants in the world.
- California: Home to the Claude “Bud” Lewis Carlsbad Desalination Plant, the largest seawater desalination facility in the Western Hemisphere, producing about 50 million gallons per day. California also operates numerous smaller brackish water facilities.
- Arizona and New Mexico: Operate brackish groundwater plants to supplement limited surface water supplies.
Coastal states in the Southeast and mid-Atlantic have generally had less pressure to invest in desalination because surface water and rainfall have historically met demand. That calculus is changing in parts of Virginia, the Carolinas, and Georgia as population growth strains existing supplies and drought patterns shift.
Brackish Versus Seawater Plants
The split between brackish and seawater desalination in the US is lopsided. Brackish plants outnumber seawater plants by a wide margin, and the reasons are straightforward. Brackish water contains far fewer dissolved salts than ocean water, which means the membranes used to filter it work under much lower pressures. Lower pressure means less energy, which means lower costs. A brackish water plant might use a third to a half of the energy per gallon that a seawater plant requires.
This energy gap is why the US has been slow to build large seawater facilities compared to countries in the Middle East or the Mediterranean. Where brackish groundwater or mildly saline aquifers exist, it has been cheaper to tap those sources first. Seawater desalination in the US has mostly been a last resort for coastal cities that have exhausted other options or face severe drought cycles. The Carlsbad plant in San Diego County, for instance, was built after decades of debate precisely because Southern California’s imported water supplies were becoming less reliable.
El Paso’s Inland Desalination Story
El Paso, Texas, offers a useful case study of how inland desalination works in practice. The Kay Bailey Hutchison Desalination Plant treats brackish groundwater from the Hueco Bolson aquifer using high-pressure membranes. After more than a decade of operation, the facility could no longer produce blended finished water at its original design capacity and had to undergo a comprehensive retrofit, including new membranes and interstage booster pumps to handle varying feedwater conditions.1Opflow. Life in the Desert Leads to Improvements at El Paso Water’s Kay Bailey Hutchison Inland Desalination Plant
One challenge that inland plants like El Paso’s face is what to do with the concentrated brine left over after desalination. Coastal plants can discharge brine back into the ocean, though that carries its own environmental concerns. Inland plants have fewer options. When El Paso expanded its treatment capacity, staff had to evaluate different strategies for managing and disposing of the concentrated waste stream.2Journal AWWA. Evaluating Brine Management Technologies in an El Paso Treatment Plant Options typically include deep-well injection, evaporation ponds, or emerging zero-liquid-discharge systems that crystallize the salts for disposal or sale. Each option adds cost, and brine management often represents a significant fraction of an inland plant’s operating budget.
Energy Use and the Cost Question
Energy is the single largest operating cost for any desalination plant. Seawater reverse osmosis, the dominant technology for ocean-fed facilities, requires pushing saltwater through semi-permeable membranes at very high pressure. Current systems use substantially more energy than the theoretical minimum needed to separate salt from water. A study analyzing data from 39 facilities found that about 69 percent of this excess energy could be eliminated using existing state-of-the-art methods, and as much as 82 percent could be cut with emerging technologies like batch reverse osmosis.3Joule. Practical minimum energy use of seawater reverse osmosis
Those numbers matter because energy cost is the main reason desalinated water is more expensive than conventional surface water or groundwater. In most US cities, desalinated seawater costs several times what treated river or reservoir water does. Brackish desalination is cheaper but still pricier than conventional treatment. This cost gap explains why desalination remains a supplemental source in most US water portfolios rather than the primary one. Utilities typically blend desalinated water with other supplies to keep average rates manageable for customers.
One approach to reducing energy costs is co-locating desalination plants with power generation stations. Sharing intake and discharge infrastructure can yield measurable savings, and the desalination plant can benefit from lower electricity costs when it draws power directly from the adjacent generator.4Filtration & Separation. Seawater desalination costs cut through power plant co-location Co-location can also provide environmental benefits, because the combined thermal and saline discharges dissipate faster when blended than when released separately.
Environmental Concerns With Coastal Facilities
Seawater desalination plants draw enormous volumes of ocean water through intake structures, and marine organisms get pulled in with it. Small fish, larvae, eggs, and plankton can be trapped against intake screens (a process called impingement) or drawn into the plant and destroyed (entrainment). The raw numbers can sound alarming. An environmental assessment for a proposed facility in Southern California projected that a plant producing roughly 45 million gallons per day would entrain over 10 million fish larvae and more than 834 million fish eggs annually.5Desalination. Environmental issues in seawater reverse osmosis desalination: Intakes and outfalls
Whether those losses translate into meaningful harm to fish populations is genuinely debated. California regulators take a conservative approach, assuming that ichthyoplankton losses significantly affect local fisheries, and the state requires new coastal plants to use subsurface intakes or equivalent technology to minimize the damage. But the same study noted that few scientific investigations actually support this assumption when natural mortality rates and reproductive capacity of the affected species are factored in. Eggs and larvae in the ocean already face staggeringly high natural mortality, so the additional losses from a desalination intake may represent a small fraction of what nature already removes.
On the discharge side, brine concentrate released into the ocean is denser and saltier than the surrounding seawater. If not properly diluted, it can create hypersaline zones on the seafloor that stress or kill bottom-dwelling organisms. Modern plants typically use diffuser systems that mix the brine rapidly with ambient seawater, reducing the footprint of the salinity plume. California and a few other states require detailed modeling and monitoring of brine discharge impacts as a condition of permitting.
Renewable Energy and the Future of US Desalination
The biggest constraint on expanding desalination in the US has been the combination of cost and carbon footprint. Running a large reverse osmosis plant on fossil-fuel electricity is expensive and produces significant greenhouse gas emissions. This is where the intersection of renewable energy and desalination is generating serious interest.
Simulations using verified models of US water, solar, and wind resources suggest that desalination powered mainly by solar and wind energy could sustainably meet the needs of the municipal, thermoelectric, and industrial sectors in water-stressed regions.6Progress in Energy. Water production by renewable energy powered desalination for meeting climate change induced water supply-demand deficits in the United States The appeal is straightforward: solar and wind costs have fallen dramatically over the past decade, and pairing them with desalination addresses both the cost barrier and the emissions problem simultaneously. Zero-liquid-discharge designs, which recover nearly all the water and leave behind only solid salt waste, are part of this vision because they reduce the environmental footprint of brine disposal.
Several pilot projects around the country are already testing solar-powered desalination at small scales. The challenge is intermittency. Desalination membranes prefer steady operating pressure, and solar and wind output fluctuates. Battery storage and flexible plant designs that can ramp up and down are part of the engineering solution, but at large scale, nobody has yet demonstrated a fully renewable-powered seawater desalination plant that runs year-round in the US. The technology is plausible, the economics are improving, and climate-driven water shortages are providing the motivation.
Why the US Has Fewer Seawater Plants Than You Might Expect
Compared to Israel, Saudi Arabia, the United Arab Emirates, Spain, or Australia, the United States has relatively few large seawater desalination facilities. This surprises people who see headlines about Western drought and water crises. The reason is not technical reluctance but economic and regulatory context. The US has historically had abundant freshwater resources relative to its population. Even drought-prone states like California still get most of their water from snowpack, reservoirs, and groundwater. Desalination has been the expensive option held in reserve.
Permitting also plays a role. Building a seawater desalination plant in California, for example, involves navigating environmental review processes that can stretch across a decade or more. The Carlsbad plant took roughly 14 years from initial proposal to operation. A proposed facility in Huntington Beach was debated for two decades before being rejected by the California Coastal Commission in 2022. The regulatory bar is high because of concerns about marine life impacts, energy use, greenhouse gas emissions, and the precedent of privatizing ocean water.
In contrast, brackish groundwater desalination faces much lighter permitting because it draws from underground aquifers rather than the ocean. This regulatory asymmetry is another reason why the US desalination landscape is dominated by smaller inland plants rather than big coastal ones.
How Desalination Fits Into US Water Supply
Even with roughly 1,500 facilities, desalination supplies a small fraction of total US water consumption. The vast majority of American drinking water still comes from surface reservoirs, rivers, lakes, and conventional groundwater wells. Desalination is most significant in places where those conventional sources are inadequate or declining. In communities like El Paso, Carlsbad, or parts of the Florida Keys, desalinated water makes up a meaningful share of the local supply. Nationally, the percentage is still in the low single digits.
That share is expected to grow. Climate change is intensifying drought in the American West and Southwest, saltwater intrusion is threatening coastal aquifers in Florida and the Gulf states, and population growth continues in some of the driest parts of the country. Water managers in these regions view desalination not as a silver bullet but as one more tool in a portfolio that includes conservation, water recycling, aquifer recharge, and inter-basin transfers. The number of US desalination plants will almost certainly continue to climb, but the growth will likely remain dominated by brackish facilities rather than headline-grabbing seawater megaprojects, because brackish treatment is cheaper, faster to permit, and meets the immediate need in most water-stressed inland communities.
Membrane Aging and Plant Maintenance
One aspect of desalination that rarely makes the news is how quickly the core technology degrades. Reverse osmosis membranes are the heart of any desalination plant, and they do not last forever. Over years of operation, membranes accumulate mineral scaling, biological fouling, and physical wear that gradually reduce their ability to reject salt and produce clean water at design flow rates. El Paso’s experience is typical: after roughly a decade, the plant’s original membranes could no longer keep up, requiring a full evaluation and replacement cycle along with new booster pumps to maintain performance under changing feedwater conditions.1Opflow. Life in the Desert Leads to Improvements at El Paso Water’s Kay Bailey Hutchison Inland Desalination Plant
Membrane replacement is a planned expense, but the timing and cost depend heavily on local water chemistry. Plants treating water with high silica, calcium, or biological content may need to replace membranes more frequently. Chemical cleaning can extend membrane life, but eventually the membranes lose enough performance that replacement becomes the only practical option. For a large facility, a full membrane swap can cost millions of dollars. This ongoing maintenance cost is something that financial projections for new desalination plants sometimes understate, leading to sticker shock for utilities a decade or so after a plant opens.