Desalination converts the planet’s most abundant water source, the ocean, into something people can actually drink, irrigate crops with, and run through industrial systems. With population growth, urbanization, and climate change squeezing conventional freshwater supplies in regions around the world, desalination has become a critical backstop against shortage. The technology is not without trade-offs in energy use, cost, and ecological impact, but its role in water security is expanding faster than almost any other supply-side strategy.
The Freshwater Squeeze
Earth holds enormous volumes of water, but the vast majority is saltwater. The freshwater that cities, farms, and ecosystems depend on comes from rivers, lakes, snowpack, and underground aquifers, all of which are under mounting pressure. Rapid population growth and urbanization are driving over-abstraction of these conventional sources, pushing many regions into what hydrologists classify as water scarcity.1PubMed Central. Is Desalination a Solution to Freshwater Scarcity in Developing Countries? Coastal aquifers alone supply water to over a billion people worldwide, yet many of these aquifers are losing ground to seawater intrusion caused by overpumping.2Hydrogeology Journal. Challenges and approaches for management of seawater intrusion in coastal aquifers
Climate change compounds the problem. Rising sea levels push saltwater further inland into coastal groundwater, and recurring droughts reduce surface water availability. In places like Southeast Florida, the combination of overpumping, drought, and sea-level rise is actively threatening the freshwater stored in the Biscayne aquifer.3Desalination. Sustainable saltwater intrusion management in coastal aquifers under climatic changes for humid and hyper-arid regions These pressures are not theoretical projections for a distant future. They are already reshaping water management decisions in the Middle East, North Africa, Australia, parts of the American West, and island nations across the Pacific and Caribbean.
Desalination steps in where conventional freshwater simply cannot keep up. Unlike rainfall or snowmelt, it does not depend on weather patterns. Unlike aquifer pumping, it does not draw down a finite underground reserve. The ocean is, for all practical purposes, an unlimited raw material. That independence from the hydrological cycle is what makes desalination strategically important, especially for regions facing chronic or worsening scarcity.
How Modern Desalination Works
Two broad families of technology dominate the desalination industry. The first is thermal distillation, which heats seawater until it evaporates and then condenses the vapor into freshwater, leaving the salt behind. Multi-stage flash distillation, the most common thermal method, accounts for roughly a third of global desalination capacity and is especially prevalent in the oil-rich Gulf states, where cheap energy and extremely salty feedwater make it practical.4PubMed Central. Water Desalination Using the Once-through Multi-Stage Flash Concept: Design and Modeling
The second family, and the one that has come to dominate new installations worldwide, is membrane-based reverse osmosis. In reverse osmosis, seawater is forced through a semi-permeable membrane at high pressure. The membrane allows water molecules to pass while blocking dissolved salts. Reverse osmosis now represents about 80 percent of all desalination plants installed globally and holds roughly 44 percent of world desalting production capacity.5PubMed Central. Reverse osmosis desalination: water sources, technology, and today’s challenges Its dominance has grown because it uses less energy than boiling water and can be adapted to different salt concentrations, from full-strength seawater to mildly brackish groundwater.
The distinction between seawater reverse osmosis and brackish water reverse osmosis matters more than most people realize. Brackish groundwater has far less salt than the ocean, so pushing it through a membrane requires much less pressure and energy. Many inland desalination plants treat brackish water rather than seawater, which keeps costs and energy consumption considerably lower.
The Energy Question
Energy is the single largest operating cost for a desalination plant, and it is the main reason critics call the technology unsustainable. Treating conventional surface water uses roughly 0.2 to 0.4 kilowatt-hours per cubic meter. A real-world seawater reverse osmosis plant, including pretreatment and post-treatment, typically consumes about 3.5 to 4.5 kilowatt-hours per cubic meter, roughly ten times as much.6Desalination. A comprehensive review of energy consumption of seawater reverse osmosis desalination plants That gap is real and significant, especially for countries already struggling with electricity generation.
The good news is that the gap has been shrinking for decades. Improvements in membrane materials, energy-recovery devices, and plant design have brought energy consumption down from around 5 kilowatt-hours per cubic meter in the 1990s to under 2 kilowatt-hours per cubic meter for the reverse osmosis stage itself in more efficient modern systems.7Desalination. A review on desalination by graphene-based biomimetic nanopore: From the computational modelling perspective That figure reflects the membrane process alone rather than the full plant, but the trajectory is encouraging.
Renewable energy is also changing the equation. About 70 percent of renewable-energy-powered desalination plants run on solar energy, with solar photovoltaic systems paired with reverse osmosis making up the largest share.8Desalination. Solar energy-driven desalination: A renewable solution for climate change mitigation and advancing sustainable development goals In sunny, water-scarce regions like the Arabian Peninsula and North Africa, the logic is almost too neat: the same geography that creates water scarcity also delivers abundant solar radiation. Techno-economic analyses of hybrid solar-and-wind-powered reverse osmosis plants have shown energy efficiencies comparable to conventional grid-powered plants, with minimal surplus power generation.9International Journal of Innovative Research and Scientific Studies. Renewable energy integration in desalination: A cost analysis of solar and wind-powered seawater RO system If desalination’s carbon footprint is its Achilles’ heel, renewables are the armor being fitted over it.
What Happens to the Brine
For every liter of freshwater a seawater reverse osmosis plant produces, it also generates a concentrated stream of brine, typically about 1.5 to 2 times saltier than the intake water, laced with the chemicals used during the treatment process. Most plants discharge this brine back into the ocean. What happens next is the biggest environmental question hanging over the industry.
Research on brine discharge has painted a complicated picture. The concentrated salt itself can harm seafloor organisms. Reviews of the literature have documented effects on bacteria, seagrasses, worms, and corals within the discharge mixing zone, ranging from impaired activity and tissue deformation to shifts in which species dominate the community.10PubMed. Impacts of Desalination Brine Discharge on Benthic Ecosystems Recent modeling has shown that brine can spread along the seabed for tens of kilometers beyond the immediate mixing zone, affecting nutrient exchange between sediment and the water column.
But salinity is not the only stressor. A study of a large-scale desalination outfall found that even when diffusers successfully diluted the brine to less than one practical salinity unit above ambient levels within 100 meters, sessile invertebrates like sponges and bryozoans still declined in cover near the outfall. The researchers concluded that changes in water flow caused by the high-pressure diffusers, not salt concentration, were likely driving much of the impact.11PubMed. First large-scale ecological impact study of desalination outfall reveals trade-offs in effects of hypersalinity and hydrodynamics This is a genuinely tricky engineering problem: the diffusers designed to dilute salt quickly create turbulence that disrupts feeding and settlement for bottom-dwelling organisms.
The chemicals in brine add another layer of concern. Antiscalants, which prevent mineral buildup on membranes, are discharged along with the brine. Polyphosphonate-based antiscalants have been shown to boost dissolved organic phosphorus at the seabed by roughly six-fold and increase microbial activity several times over compared to unaffected areas.12Environmental Science & Technology. Discharge of Polyphosphonate-Based Antiscalants via Desalination Brine: Impact on Seabed Nutrient Flux and Microbial Activity In nutrient-poor waters, antiscalants can act as a fertilizer for microbes, shifting microbial communities in ways that are not yet fully understood.13PubMed Central. Antiscalants Used in Seawater Desalination: Biodegradability and Effects on Microbial Diversity
Corals are a particularly sensitive indicator. Laboratory experiments exposing the coral Montipora capricornis to antiscalants found that both polymer-based and polyphosphonate-based formulations reduced polyp activity by about a quarter and caused significant tissue damage within two weeks. The polyphosphonate type also depleted the coral’s symbiotic algae by close to 40 percent.14PubMed. Antiscalants used in the desalination industry impact the physiology of the coral Montipora capricornis For countries building desalination plants along coastlines that also host coral reefs, the choice of antiscalant formulation is not trivial.
Desalinated Water Is Not Immediately Ready to Drink
A common misconception is that once salt is removed, desalinated water is good to go. It is not. Water that emerges from a reverse osmosis membrane is almost completely stripped of dissolved minerals. It is slightly acidic, has very low buffering capacity, and is corrosive to metal and concrete pipes.15Desalination. Remineralization of desalinated water: Methods and environmental impact If sent directly into a distribution network, it would eat away at the infrastructure and leach metals into the water supply.
Every desalination plant that produces drinking water includes a remineralization step as the final stage of treatment. This process reintroduces calcium, alkalinity, and adjusts the pH so the water reaches a stable equilibrium that will not dissolve or deposit calcium carbonate in pipes.16IntechOpen. Remineralization and Stabilization of Desalinated Water The result is water that meets drinking-water standards and behaves predictably inside distribution systems. Getting the mineral balance right also matters for taste. Ultrapure water tastes flat and unpleasant to most people, so a small amount of mineral content is both a health and a palatability requirement.
Farming with Desalinated Water
Agriculture consumes far more water than cities do, so expanding desalination into irrigation could have enormous implications. Reverse osmosis permeate has very low dissolved solids, typically below 250 milligrams per liter, and an electrical conductivity below 0.5 deciSiemens per meter. When it replaces low-quality irrigation water, crops experience less salinity stress, and yields and quality can improve.17Desalination. Seawater desalination for crop irrigation — A review of current experiences and revealed key issues
In practice, though, farmers rarely irrigate with pure desalinate. The same corrosiveness that makes it risky for pipes makes it unsuitable for soils, which need some mineral content to maintain structure. Blending desalinated water with conventional water sources is the more common approach. Israel, one of the world’s heaviest users of desalination, blends desalinated water into its national water system, so the water reaching farms is a mix rather than pure permeate. The economic barrier is also real: desalinated water remains more expensive than most conventional irrigation supplies, so its agricultural use tends to be concentrated in high-value crops or regions where no cheaper alternative exists.
Desalination Compared to Water Recycling
Desalination is not the only option for stretching a limited water supply. Direct potable water reuse, in which treated wastewater is purified and returned to the drinking supply, is a growing competitor. An economic comparison of three scenarios for increasing a coastal city’s water supply by 50 percent found that direct potable reuse and a hybrid forward-osmosis/reverse-osmosis configuration both came in around $0.59 to $0.61 per cubic meter, while straight seawater desalination cost about $0.67 per cubic meter, roughly 12 percent more.18PubMed. Augmenting water supply by combined desalination/water recycling methods: an economic assessment
That cost difference is modest, and in practice the choice depends on local conditions. Water recycling requires a steady supply of wastewater, which means it works best in large, densely populated urban areas. It also faces public perception challenges, since people tend to be more squeamish about purified wastewater than about desalinated seawater, even when the end product is chemically equivalent. Desalination, on the other hand, works well wherever you have coastline and energy. Most water planners increasingly see the two as complementary rather than competing: recycling handles the inland and wastewater-rich scenarios, desalination covers the coastal ones, and both reduce pressure on natural freshwater sources.
Brine as a Resource, Not Just a Waste Stream
The industry is beginning to treat brine less as a disposal problem and more as a raw material. The zero-liquid-discharge framework aims to recover virtually all the freshwater from brine and extract commercially valuable minerals from what remains. A somewhat less ambitious cousin, minimal liquid discharge, can recover up to 95 percent of the freshwater from brine at lower energy and capital costs than full zero-liquid discharge.19Desalination. Waste to wealth: A critical analysis of resource recovery from desalination brine
Researchers have also explored using concentrated brine as a feedstock for energy generation. A hybrid system combining reverse electrodialysis with forward osmosis demonstrated the possibility of generating salinity-gradient power from high-salinity brine and low-salinity wastewater, while also producing a diluted stream suitable for fertigation.20Desalination. Potential application of hybrid reverse electrodialysis (RED)-forward osmosis (FO) system to fertilizer-producing industrial plant for efficient water reuse Extracting lithium, magnesium, and other valuable elements from concentrated brine is another area of active research. None of these approaches are yet widespread at commercial scale, but they point toward a future in which desalination waste becomes a revenue stream rather than an environmental liability.
The Geopolitical Dimension
Water scarcity is a well-known driver of tension between countries that share rivers and aquifers. You might assume that desalination, by creating an entirely new water source independent of shared resources, would ease those tensions. The reality is more nuanced.
An analysis of how desalination has affected transboundary water relations found mixed results. In the case of Cyprus and Northern Cyprus, cooperation between the parties increased after desalination capacity was built. But in the Israeli-Palestinian and Israeli-Jordanian cases, cooperation actually declined after desalination was introduced.21Journal of Environmental Management. Desalination and transboundary water governance in conflict settings The mechanism is counterintuitive: when a country can meet its water needs unilaterally through desalination, it has less incentive to negotiate over shared water resources. That reduces the diplomatic leverage of the water-scarce party and can make broader cooperation harder, not easier.22Environmental Science & Policy. Desalination and hydrodiplomacy: Refreshening transboundary water negotiations or adding salt to the wounds?
Desalination can also create new disputes. Access to previously unusable water sources, rights to coastal zones for plant siting, and the environmental effects of brine discharge across maritime boundaries all introduce fresh points of contention. For water diplomats, desalination is a tool that changes the negotiating landscape rather than simply defusing it.
Who Relies on Desalination the Most
The geography of desalination tracks the geography of water stress, but it is not a perfect overlap because energy cost matters so much. The Persian Gulf states, especially Saudi Arabia, the United Arab Emirates, Kuwait, and Qatar, are the world’s heaviest users. These countries combine extreme aridity with access to cheap energy, making desalination economically viable even at massive scales. Israel draws a significant share of its municipal water from desalination and is often cited as a model for integrating desalinated water into a national grid. Australia built several large plants during the Millennium Drought, though some have since been mothballed as reservoirs refilled. Singapore, with essentially no natural freshwater of its own, treats desalination as a pillar of national survival alongside water recycling and imported water from Malaysia.
Smaller island nations in the Caribbean and Pacific increasingly depend on desalination as well, though they face a tougher economic picture: limited local energy production, small populations to share costs, and aging infrastructure. For these communities, solar-powered desalination units represent a particularly promising path forward, since they sidestep the imported fuel costs that dominate operating budgets.
Countries in sub-Saharan Africa and South Asia, where water scarcity is severe but energy infrastructure is weak and capital is scarce, have seen far less desalination development. Membrane-based desalination technology is increasingly finding outlets in these water-scarce regions, but deployment remains uneven.1PubMed Central. Is Desalination a Solution to Freshwater Scarcity in Developing Countries? The challenge is not technological availability so much as the financing, grid reliability, and technical workforce needed to operate plants over the long term.
Cost Trends and Where They Are Heading
Desalinated water has historically been expensive. In the early days of reverse osmosis, costs for seawater desalination ran around four dollars per thousand gallons. Engineering analyses at the time predicted that optimized two-stage systems could bring that figure down by 40 percent, to roughly $2.60 per thousand gallons.23Desalination. Means by which reverse osmosis desalting costs can be substantially reduced well before the year 2000 Those predictions proved roughly correct and then some. Modern large-scale plants in competitive markets like Israel and Saudi Arabia have pushed costs below one dollar per cubic meter in some contracts, driven by better membranes, larger plant scales, energy-recovery technology, and competitive bidding.
The cost trajectory matters because it determines whether desalination remains a last resort or becomes a routine part of the water supply portfolio. As the price per cubic meter continues to drop, and as the cost of conventional water rises due to scarcity premiums, infrastructure investment, and treatment of increasingly polluted sources, the gap between desalinated and conventional water narrows. In some coastal cities, the crossover point has already arrived: desalinated water is competitive with the marginal cost of developing the next conventional water source. That shift quietly changes the economics of everything from urban planning to agricultural policy.