Desalination works, and it already supplies drinking water to hundreds of millions of people, but a combination of high energy costs, expensive infrastructure, environmental side effects, and the simple geography of where people live keeps it from becoming the default answer to water scarcity. Roughly 16,000 desalination plants operate worldwide, producing around 95 million cubic meters of freshwater per day, yet nearly half of that output is concentrated in the Middle East and North Africa.1PubMed. The state of desalination and brine production: A global outlook For most of the world, cheaper alternatives still exist, and the barriers to scaling desalination remain stubbornly real.
Energy Is the Core Bottleneck
Turning saltwater into freshwater takes a lot of energy, and energy is the single largest operating cost for any desalination plant. The dominant technology today is reverse osmosis (RO), which forces seawater through a membrane under high pressure to separate salt from water. RO has steadily improved in efficiency and now uses far less energy than the older thermal approaches, which essentially boil seawater and collect the steam. But even the most efficient modern RO plants consume substantial electricity per cubic meter of water produced.
Thermal desalination, including multi-stage flash and multi-effect distillation, demands even more energy and carries higher maintenance costs, which generally makes it less attractive than RO.2Desalination. Energy for desalination: A state-of-the-art review So why does anyone still use it? In the Persian Gulf states, where oil is cheap, algae blooms frequently clog RO membranes, and the seawater itself is unusually salty and turbid, thermal plants remain the practical choice.2Desalination. Energy for desalination: A state-of-the-art review That regional quirk illustrates a broader reality: the “best” desalination technology depends heavily on local conditions, and no single solution works everywhere.
The energy problem also carries a carbon problem. Most desalination plants run on fossil fuel-generated electricity, which means every liter of desalinated water comes with a greenhouse-gas cost. For countries trying to meet climate targets, building large-scale desalination powered by coal or natural gas creates a tension between water security and emissions reduction.
The Price Tag Compared to Conventional Water
Large-scale desalination plants can produce water in a range of roughly $0.50 to $2.00 per cubic meter, depending on plant size and technology.3Desalination. Estimating the cost of desalination plants using a cost database That may not sound like much until you compare it to what conventional water sources cost. Groundwater pumping, river diversions, and reservoir storage typically deliver water for a fraction of that price in regions where fresh surface water or aquifers are available. Even in semi-arid areas, conservation measures and water recycling tend to be cheaper per cubic meter than building a new desalination plant.
A cost analysis in Israel, one of the countries most committed to desalination, found that desalination ranked among the least cost-efficient options compared to demand management and other supply strategies, even before factoring in environmental externalities. That finding undercuts the narrative that desalination is the obvious answer for water-scarce nations. It can be the right answer when other options have been exhausted, but it is rarely the cheapest one.
Brackish water, which is salty but far less so than seawater, offers a middle ground. Brackish-water RO plants operate at lower pressures and therefore lower energy costs, with operating expenses in the range of roughly $0.39 to $0.66 per cubic meter for mid-to-large-scale facilities.4PubMed Central. Economics and Energy Consumption of Brackish Water Reverse Osmosis Desalination: Innovations and Impacts of Feedwater Quality But brackish groundwater has its own catch: sustained pumping often pulls in saltier water over time, gradually increasing both energy use and treatment costs.4PubMed Central. Economics and Energy Consumption of Brackish Water Reverse Osmosis Desalination: Innovations and Impacts of Feedwater Quality
Geography Makes Inland Desalination Impractical
Most of the world’s water-stressed populations do not live on the coast. Getting desalinated water from a shoreline plant to an inland city means pumping it across long distances and, often, uphill. The cost of that transport is a barrier all by itself. Research has shown that lifting water 100 meters vertically costs about the same as moving it 100 kilometers horizontally, roughly $0.05 to $0.06 per cubic meter.5Water Resources Research. Evaluating the costs of desalination and water transport For a city at sea level 50 kilometers from the coast, that adds a manageable surcharge. For a highland city hundreds of meters above sea level and deep in a continental interior, transport costs can double or triple the price of the water itself, making desalination prohibitively expensive.5Water Resources Research. Evaluating the costs of desalination and water transport
One creative approach is to distribute the desalination process itself across different elevations, placing RO stages closer to where the water is actually needed rather than concentrating everything at sea level. This can reduce the total energy needed for both desalination and transport.6Applied Water Science. Elevation-distributed multistage reverse osmosis desalination with seawater pumped storage It is an elegant engineering concept, but it requires building and maintaining multiple treatment facilities instead of one large plant, which adds its own complexity and cost. For places like Nairobi, Mexico City, or Addis Ababa, desalination remains largely irrelevant because of sheer distance from the ocean.
What the Brine Does to Marine Ecosystems
Every cubic meter of freshwater a desalination plant produces leaves behind a concentrated stream of brine, typically one-and-a-half to two-and-a-half times saltier than the surrounding seawater.7Current Opinion in Environmental Science & Health. Impact of brine discharge from desalination plants on marine ecosystems: A review When this brine is dumped back into the ocean, it sinks because it is denser than normal seawater, creating a zone of elevated salinity on the seafloor near the discharge point. The ecological damage from this concentrated discharge can be significant.
A review of the research found that brine harms marine life at multiple levels. Seagrass meadows exposed to high salinity show reduced photosynthesis and leaf damage. Shellfish and other bottom-dwelling creatures, which cannot easily move away, experience physiological stress and population declines. Fish in affected areas show impaired growth and reproductive problems. Coral reefs face lower calcification rates and increased vulnerability to bleaching. Brine also carries residual treatment chemicals and trace metals that can accumulate in organisms and move up the food chain.7Current Opinion in Environmental Science & Health. Impact of brine discharge from desalination plants on marine ecosystems: A review Thermal plants add an extra layer of harm because their discharge is also warmer than ambient seawater, reducing dissolved oxygen and further stressing organisms.8Desalination. Ecotoxicological marine impacts from seawater desalination plants
The picture is not uniformly bleak, though. A field study on South America’s Pacific coast found that with proper diffuser design and a well-chosen discharge location, the salinity increase stayed below about 3.5 percent above natural levels within 50 meters of the outfall. Marine organisms exposed to the brine did show stress responses initially, but antioxidant and osmotic markers recovered fully within five days.9PubMed. Evaluating physico-chemical and biological impacts of brine discharges for a sustainable desalination development on South America’s Pacific coast Good engineering and site selection can mitigate the damage substantially, but many older plants were built without these precautions, and environmental permitting for new plants can be lengthy and contentious.
Beyond brine, the intake side of a desalination plant also harms marine life. Open-ocean intakes suck in large volumes of seawater and, along with it, fish larvae, plankton, and other small organisms. Larger creatures get trapped against intake screens, while smaller ones pass through and are killed during processing.10Desalination. Environmental issues in seawater reverse osmosis desalination: Intakes and outfalls Subsurface intakes and screens with finer mesh can reduce this problem, but they add cost and are not feasible at every site.
The Water That Comes Out Is Not Ready to Drink
A fact that surprises many people: the freshwater produced by desalination is too pure to use directly. It is slightly acidic, almost devoid of minerals, and corrosive to pipes and infrastructure. Left untreated, it would leach metals from plumbing, degrade distribution networks, and deliver water that lacks minerals beneficial to human health.11Desalination. Remineralization of desalinated water: Methods and environmental impact Every desalination plant therefore needs a remineralization step, adding calcium, magnesium, and alkalinity back into the water before it enters the supply system.
Remineralization is a solved engineering problem, but it adds another layer of cost and complexity that conventional water treatment does not require. It also means the final water quality depends on how well the remineralization step is designed and maintained. In developing countries or remote locations where technical expertise is limited, this extra processing step is a real barrier to building and operating desalination reliably.
Why Solar-Powered Desalination Has Not Taken Off
Pairing desalination with solar energy sounds like a perfect marriage, especially in sun-drenched, water-scarce regions. In practice, the intermittent nature of solar power creates serious operational problems. RO membranes do not like being turned on and off. Each startup-shutdown cycle stresses the system, and running at partial load reduces efficiency. A solar-powered RO plant is also limited by cloudy days and nighttime, which either means the plant sits idle or requires battery storage, adding substantially to the cost.12Journal of Sustainable Development of Energy, Water and Environment Systems. Solar Desalination: Current Applications and Future Potential in MENA Region
These challenges are not insurmountable. Hybrid systems that combine solar with grid power or with energy storage are being tested and deployed. But for now, the added expense of managing intermittency keeps solar-powered desalination from competing with grid-powered plants on cost, which means the carbon problem described earlier persists for most large installations.
Membrane Technology Is Improving but Not There Yet
The membranes used in RO are the heart of modern desalination, and researchers have been working on next-generation materials, including graphene-based membranes, carbon nanotubes, and metal-organic frameworks, that could theoretically allow water through faster while blocking salt more effectively. The promise is real: these materials have intrinsic structures that could dramatically improve both water flow and salt rejection.
The gap between laboratory results and real-world performance, however, remains wide. In actual applications, these novel membranes fall short of their theoretical potential, and challenges around large-scale manufacturing, mechanical durability, and chemical stability still limit their practicality.13PubMed Central. Next-Generation Desalination Membranes Empowered by Novel Materials: Where Are We Now? Conventional polyamide thin-film composite membranes, the workhorses of the industry since the 1980s, continue to dominate because they are cheap to produce, well understood, and reliable at scale.14Membrane Technology. Desalination by distillation and by reverse osmosis — trends towards the future A breakthrough membrane could change the economics of desalination substantially, but the industry has been waiting for that breakthrough for over a decade.
Hybrid approaches that combine forward osmosis with reverse osmosis show some promise for reducing energy consumption. In simulations, certain configurations achieved energy use below 1 kilowatt-hour per cubic meter for the RO stage, lower than conventional standalone RO.15Desalination. Can a forward osmosis-reverse osmosis hybrid system achieve 90% wastewater recovery and desalination energy below 1 kWh/m³? Forward osmosis uses natural osmotic pressure differences to pre-dilute salty water before it reaches the RO stage, reducing the work the RO system has to do.16PubMed Central. Energy Efficient Forward Osmosis to Maximize Dewatering Rates These hybrid systems are still largely experimental, but they represent one of the more plausible paths to meaningfully cheaper desalination.
Community Opposition and Siting Conflicts
Even when the economics work and the environmental impact can be managed, desalination projects frequently run into public opposition. Coastal communities resist having industrial plants built on their shorelines. Environmental groups challenge permits over brine discharge and marine-life impacts. Fishers worry about intake effects on local fish populations. These conflicts can delay projects for years or kill them entirely.17Sustainable Desalination Handbook. Social Issues and Public Acceptance of Seawater Desalination Plants
The political dynamics vary enormously by region. In Gulf states, where freshwater alternatives barely exist and governments can direct large infrastructure projects with minimal public opposition, desalination scaled rapidly. In the United States, where the federal government initially championed desalination research for the arid Southwest, the technology was ultimately exported to the Middle East rather than deployed domestically. Cold War-era technical assistance programs redirected American desalination expertise to Israel and Saudi Arabia, and the U.S. lost its early lead in the field.18Environment and History. Desert Dreams of Drinking the Sea, Consumed by the Cold War California, the original target for American desalination, did not open its first major seawater plant until 2015, after decades of proposals, lawsuits, and regulatory battles.
Mining Brine for Valuable Minerals
One of the more interesting ideas for improving desalination’s economics is to treat the brine not as waste but as a resource. Seawater contains dissolved minerals like lithium, magnesium, strontium, and rubidium, all of which have commercial value. After desalination concentrates these minerals in the reject brine, extracting them becomes more feasible than pulling them from dilute seawater.
A study of Spanish desalination plants estimated that the minerals recoverable from their brine output, including boron, calcium, magnesium, lithium, rubidium, and gallium, could have a total economic value between roughly 13 and 30 billion euros per year. Even focusing only on the most valuable elements, which represent just 0.1 percent of the total brine volume, the potential revenue was estimated at around 3.8 billion euros per year.19Desalination. The economic value of the extracted elements from brine concentrates of Spanish desalination plants These are theoretical maximums, not what current extraction technology can deliver profitably. But as demand for lithium and other battery materials grows, brine mining could offset some of desalination’s costs and reduce the volume of concentrated waste discharged to the ocean.
Where Desalination Makes the Most Sense Despite Everything
For all its drawbacks, desalination is not going away. It thrives in places where the alternatives are worse: island nations with no freshwater aquifers, Gulf states with almost no rainfall, and coastal megacities that have already maxed out their conventional water supplies. Singapore, Israel, and several Australian cities have built desalination into their water portfolios as drought insurance, accepting the higher cost in exchange for a supply that does not depend on weather patterns.
Small island communities may represent the frontier where desalination has the most to offer per person. Many remote islands rely on rainwater catchment or imported water, both of which are unreliable. Off-grid desalination technologies powered by solar energy, including simple passive devices that use sunlight to evaporate and condense seawater, are being explored as low-cost solutions for these vulnerable populations.20Desalination. Demand for off-grid desalination technology in small-island communities These devices would not supply a city, but for a village of a few hundred people on a Pacific atoll, even a small daily output of fresh water is transformative. The technology does not need to beat urban-scale economics; it just needs to beat the cost of shipping bottled water by boat.
The pattern that emerges is that desalination fills gaps rather than replacing existing systems. It is the option you turn to when rivers run dry, aquifers are depleted, and conservation has reached its limits. For much of the world, those limits have not yet been reached, which is the most fundamental reason desalination has not spread further. It is not that the technology does not work. It is that, for most places, something cheaper and simpler still does.