Water desalination technologies explained: reverse osmosis, electrodialysis, and emerging methods

The global desalination market surpassed $20 billion in 2024 and is projected to reach $32 billion by 2030, growing at roughly 8% annually as water stress intensifies across every inhabited continent (Global Water Intelligence, 2025). More than 21,000 desalination plants now operate in over 170 countries, producing approximately 120 million cubic meters of freshwater per day. By 2025, an estimated 1.8 billion people live in regions facing absolute water scarcity, while two-thirds of the global population experiences water-scarce conditions for at least one month annually (United Nations Water, 2024). Desalination has moved from a last-resort technology deployed primarily in the Persian Gulf to a mainstream infrastructure solution, yet energy intensity, brine disposal, and cost remain defining challenges that separate viable deployments from stranded assets.

Why It Matters

Freshwater accounts for only 2.5% of Earth's total water volume, and less than 1% is accessible for human use. Climate change is compressing that supply further: the Intergovernmental Panel on Climate Change (IPCC) projects that each degree of global warming will reduce renewable water resources by an additional 20% for at least 7% of the world's population (IPCC AR6, 2023). Meanwhile, global water demand is rising by roughly 1% per year, driven by population growth, urbanization, and agricultural intensification.

Traditional water sources are failing under this pressure. Groundwater aquifers in California's Central Valley, India's Punjab region, and the North China Plain are depleting faster than natural recharge can replenish them. Surface water reservoirs across the Mediterranean, Middle East, and southern Africa face declining inflows as precipitation patterns shift. In this context, desalination offers a climate-independent water supply: the ocean does not run dry during droughts.

The economic consequences of water scarcity are enormous. The World Bank estimates that water scarcity, exacerbated by climate change, could cost some regions up to 6% of GDP by 2050 through impacts on agriculture, health, and income. Cities that invest in desalination infrastructure gain resilience against these losses, though the technology brings its own environmental and financial trade-offs that require careful management.

Key Concepts

Reverse Osmosis (RO)

Reverse osmosis is the dominant desalination technology, accounting for approximately 69% of global installed capacity (International Desalination Association, 2024). The process forces saline water through semi-permeable membranes at high pressure, typically 55 to 82 bar for seawater applications. Water molecules pass through the membrane while dissolved salts and contaminants are rejected, producing permeate with total dissolved solids (TDS) below 500 mg/L.

Modern RO membranes achieve salt rejection rates exceeding 99.8% and recovery rates of 40 to 50% for seawater, meaning roughly half the intake water becomes freshwater. Brackish water RO operates at lower pressures (10 to 25 bar) and achieves higher recovery rates of 75 to 90%, making it significantly cheaper per cubic meter.

Energy recovery devices (ERDs) have transformed RO economics. Pressure exchangers manufactured by companies like Energy Recovery Inc. capture hydraulic energy from the concentrated brine stream and transfer it to incoming feedwater, reducing net energy consumption by up to 60%. State-of-the-art seawater RO plants now operate at 2.5 to 3.5 kWh per cubic meter, approaching the theoretical thermodynamic minimum of approximately 1.06 kWh/m3 for seawater at 35 g/L salinity.

Thermal Desalination

Thermal processes, including multi-stage flash distillation (MSF) and multi-effect distillation (MED), heat saline water to produce steam that is then condensed into freshwater. These technologies dominated the desalination industry before RO matured and still account for roughly 25% of global capacity, concentrated primarily in the Persian Gulf where waste heat from power plants provides low-cost thermal energy.

MSF operates by reducing pressure across sequential stages, causing flash evaporation at progressively lower temperatures. MED uses a series of evaporator vessels (effects) at decreasing pressures, with each stage reusing the heat from the previous one. Both technologies are energy-intensive, consuming 10 to 80 kWh equivalent per cubic meter depending on the heat source, but they handle high-salinity and high-temperature feedwater better than membranes and produce very high purity distillate.

Electrodialysis (ED) and Electrodialysis Reversal (EDR)

Electrodialysis uses an electric field to pull dissolved ions through alternating anion- and cation-exchange membranes, separating salt from water. Unlike RO, which pushes water through membranes and leaves salt behind, ED moves the salt while the water stays in place. This approach is most efficient for brackish water with TDS between 1,000 and 5,000 mg/L, where energy consumption scales linearly with salinity.

EDR periodically reverses the polarity of the electrodes, which helps prevent membrane scaling and fouling without chemical cleaning. ED/EDR systems consume 0.5 to 2.5 kWh/m3 for brackish water, making them competitive with or superior to RO for lower-salinity applications. The technology is widely used in industrial water treatment, food processing, and inland brackish water desalination where brine disposal is constrained.

Emerging Technologies

Forward osmosis (FO) uses a concentrated draw solution to pull water naturally across a membrane from the feed side, driven by the osmotic pressure difference rather than applied hydraulic pressure. The draw solute must then be separated from the product water, which requires energy. FO operates at lower pressures than RO, reducing membrane fouling and potentially lowering energy costs when paired with low-grade waste heat for draw solute recovery. Commercial FO systems from companies like Porifera and Trevi Systems are deployed in niche applications including food concentration and industrial wastewater treatment, though large-scale municipal deployment remains limited.

Solar desalination encompasses multiple approaches that use solar energy directly for water purification. Solar stills and humidification-dehumidification (HDH) systems use thermal energy to evaporate and condense water. More advanced systems couple photovoltaic panels with RO units, while interfacial solar evaporation uses photothermal materials floating on water surfaces to generate steam with reported solar-to-vapor efficiencies exceeding 90% in laboratory settings (Nature Water, 2024). Companies like SunCulture and Desolenator have deployed solar-powered desalination units for off-grid communities.

Membrane distillation (MD) combines thermal and membrane processes, using a temperature difference across a hydrophobic membrane to drive water vapor from hot feed to cold permeate. MD can operate at lower temperatures (40 to 80°C) than conventional thermal processes, making it suitable for coupling with solar thermal collectors, geothermal heat, or industrial waste heat. The technology handles high-salinity brines that foul RO membranes, positioning it as a complementary treatment for brine concentration and zero-liquid discharge applications.

How It Works

A typical seawater RO desalination plant follows a multi-stage process. Raw seawater is drawn through intake structures, either open ocean intakes with screens or subsurface intakes using beach wells or infiltration galleries. Pretreatment removes suspended solids, biological matter, and scaling precursors through coagulation, flocculation, media filtration, and ultrafiltration membranes. Antiscalant chemicals prevent mineral deposits on RO membranes.

The pretreated water then enters high-pressure pumps that force it through spiral-wound RO membrane elements arranged in pressure vessels. Each vessel typically contains six to eight membrane elements in series. Large plants operate with multiple parallel trains, each producing 10,000 to 50,000 m3/day. Permeate undergoes post-treatment including remineralization with calcium and magnesium, pH adjustment, and disinfection before entering the distribution network.

The concentrated brine, containing roughly double the salinity of the intake seawater plus rejected contaminants, is discharged through ocean outfalls designed to maximize dilution and minimize ecological impact. Brine typically exits at 65 to 85 g/L TDS and may contain residual pretreatment chemicals, creating localized hypersaline zones near discharge points that require careful environmental management.

What's Working

Energy consumption has dropped dramatically. Seawater RO energy requirements fell from over 20 kWh/m3 in the 1970s to 2.5 to 3.5 kWh/m3 in modern plants equipped with isobaric energy recovery devices (International Desalination Association, 2024). This 85% reduction has been the single largest driver of desalination cost declines and geographic expansion.

Costs continue to fall. The Sorek B plant in Israel, operated by IDE Technologies, secured a water purchase agreement at $0.41/m3 when it began operations in 2024, among the lowest seawater desalination costs globally. The Taweelah plant in Abu Dhabi, developed by ACWA Power with a capacity of 909,000 m3/day, achieved contract pricing of approximately $0.49/m3. These prices approach the cost of conventional water treatment in water-scarce regions, making desalination economically competitive rather than merely a premium alternative.

Renewable energy integration is accelerating. Saudi Arabia's NEOM project includes plans for solar-powered desalination at industrial scale as part of its broader renewable energy strategy. In Australia, the Sydney Desalination Plant operates on 100% renewable electricity through offset agreements, and Perth's two desalination plants source power from dedicated wind farms. The coupling of solar photovoltaics with RO is particularly attractive in sun-rich, water-scarce regions where the peak solar generation period coincides with peak water demand.

Membrane technology keeps improving. Thin-film nanocomposite membranes incorporating graphene oxide, carbon nanotubes, or aquaporin proteins demonstrate higher permeability and selectivity in pilot testing (Werber et al., Water Research, 2024). DuPont Water Solutions and Toray Industries have released commercial membranes with 15 to 20% higher flux than previous generations, enabling either smaller plant footprints or lower operating pressures.

What Isn't Working

Brine disposal remains the industry's largest environmental liability. Conventional ocean discharge creates hypersaline plumes that damage benthic ecosystems, with studies documenting reduced biodiversity within 100 to 200 meters of outfall diffusers (Cambridge University Press, 2025). Inland plants face even greater challenges, as brine cannot simply be returned to the ocean. Evaporation ponds consume large land areas, deep well injection raises groundwater contamination concerns, and zero-liquid discharge systems add 50 to 100% to total plant costs.

Energy intensity limits deployment in power-constrained regions. Despite efficiency gains, a 100,000 m3/day seawater RO plant still requires roughly 25 to 35 MW of continuous power. In developing countries where grid reliability is poor and electricity costs are high, this demand creates a significant barrier. Desalination can account for 30 to 50% of total energy consumption in small island nations and arid city-states that rely heavily on the technology.

Membrane fouling drives operating costs. Biological fouling, mineral scaling, and particulate deposition on RO membranes require regular chemical cleaning (every 4 to 12 weeks) and membrane replacement (every 5 to 7 years). Fouling reduces permeate quality, increases energy consumption by raising required operating pressures, and accounts for an estimated 20 to 30% of total operating costs. Feedwater with high organic content, warm temperatures, or algal bloom exposure exacerbates the problem.

Emerging technologies struggle to scale. Forward osmosis, membrane distillation, and solar desalination have demonstrated promise in laboratory and pilot settings but face persistent challenges in scaling to municipal capacities. FO draw solute regeneration adds energy cost and complexity. MD flux rates remain 5 to 10 times lower than RO, requiring proportionally larger membrane areas. Solar desalination output is inherently variable and typically limited to <100 m3/day per installation, insufficient for urban supply.

Key Players

Established Leaders

• Veolia Water Technologies - global water treatment leader operating desalination plants across 40+ countries with combined capacity exceeding 7 million m3/day
• IDE Technologies - Israeli company behind the world's largest and lowest-cost SWRO plants including Sorek and Sorek B
• ACWA Power - Saudi developer and operator of the Taweelah plant (909,000 m3/day), one of the world's largest RO facilities
• Dupont Water Solutions - major manufacturer of FilmTec RO membranes used in an estimated 40% of global desalination plants
• Toray Industries - Japanese membrane manufacturer supplying high-performance RO elements globally

Emerging Startups

• Gradiant - MIT spinoff commercializing carrier gas extraction and counter-flow RO for high-recovery desalination and brine treatment
• Desolenator - Dutch company deploying solar thermal desalination units for off-grid communities in Kenya and the UAE
• Oneka Technologies - Canadian startup using wave-powered desalination buoys for coastal communities

Key Investors and Funders

• Breakthrough Energy Ventures - investing in next-generation water technology startups
• World Bank Group - financing large-scale desalination infrastructure in MENA, South Asia, and sub-Saharan Africa
• Saudi Water Authority (SWCC) - operating the world's largest desalination portfolio and funding innovation through its R&D program

Sector-Specific KPI Benchmarks

KPI	Seawater RO	Brackish Water RO	Electrodialysis	Thermal (MSF/MED)
Energy consumption (kWh/m3)	2.5 to 3.5	0.5 to 2.5	0.5 to 2.5	10 to 80 (thermal equiv.)
Water cost ($/m3)	0.40 to 1.50	0.20 to 0.80	0.30 to 1.00	0.80 to 2.50
Recovery rate (%)	40 to 50	75 to 90	80 to 95	25 to 50
Salt rejection (%)	>99.5	>98	50 to 95 (per pass)	>99.9
Membrane life (years)	5 to 7	5 to 10	5 to 10	N/A
Typical plant capacity (m3/day)	10,000 to 900,000+	1,000 to 100,000	500 to 50,000	10,000 to 800,000
Pretreatment complexity	High	Moderate	Low to moderate	Low
Brine salinity (g/L)	65 to 85	5 to 30	5 to 30	65 to 85

Action Checklist

• Characterize your feedwater source by testing salinity, temperature, turbidity, organic content, and specific ion concentrations to determine which desalination technology best fits your application
• Conduct a full lifecycle cost analysis including capital expenditure, energy costs, membrane replacement, chemical consumption, brine disposal, and maintenance over a 20 to 25 year project horizon
• Evaluate energy supply options including grid power pricing, on-site renewable generation, waste heat availability, and power purchase agreement structures that affect long-term operating economics
• Assess brine management requirements by modeling discharge volumes and concentrations, mapping available disposal options (ocean outfall, evaporation ponds, deep well injection, or zero-liquid discharge), and estimating associated environmental permitting timelines
• Engage regulatory authorities early to understand permitting requirements for water extraction, brine discharge, environmental impact assessment, and water quality standards applicable to your jurisdiction
• Pilot test membrane systems at representative scale using actual site feedwater for a minimum of 3 to 6 months to validate performance projections and identify fouling or scaling risks before committing to full-scale construction
• Develop a membrane fouling management plan including pretreatment optimization, cleaning-in-place protocols, membrane autopsy scheduling, and replacement budgeting

FAQ

Q: How does seawater RO desalination cost compare to conventional water treatment? A: Modern seawater RO produces water at $0.40 to $1.50/m3, depending on plant size, energy costs, and location. Conventional surface water treatment typically costs $0.10 to $0.50/m3. In water-scarce regions where source water must be transported long distances or aquifers are depleting, desalination can be cost-competitive or even cheaper than alternatives. Brackish water RO at $0.20 to $0.80/m3 often competes directly with conventional treatment.

Q: What is the environmental impact of brine discharge? A: Brine from seawater RO plants is typically twice the salinity of intake water and may contain residual treatment chemicals. Ocean discharge creates localized hypersaline zones that can reduce marine biodiversity near outfall points. Well-designed diffuser systems achieve rapid dilution, limiting measurable impacts to within 100 to 200 meters of the discharge. Inland plants face greater challenges and may require evaporation ponds or zero-liquid discharge systems that add 50 to 100% to costs.

Q: Can desalination run entirely on renewable energy? A: Yes. Multiple large-scale plants already operate on 100% renewable electricity, including Perth's Southern Seawater Desalination Plant (powered by a dedicated wind farm) and solar-powered facilities under development in Saudi Arabia. The intermittency of solar and wind generation requires either battery storage, grid interconnection, or flexible plant operation, but the technical feasibility is proven at commercial scale.

Q: How long do RO membranes last and what affects their lifespan? A: Commercial RO membranes typically operate for 5 to 7 years before replacement, though some installations achieve 8 to 10 years with excellent pretreatment and maintenance. Factors shortening membrane life include biological fouling, chlorine exposure, abrasive particles, and high operating pressures. Regular cleaning-in-place (CIP) with acid and alkaline solutions extends useful life but adds to operating costs.

Q: Is forward osmosis ready for large-scale deployment? A: Not yet for municipal water supply. Forward osmosis has found commercial niches in food concentration, emergency water supply, and industrial wastewater treatment, but the need to regenerate the draw solution adds energy cost and system complexity. Current FO installations are typically below 1,000 m3/day. The technology may become more competitive as draw solution recovery processes improve and when waste heat is available for regeneration.

Sources

• Global Water Intelligence. (2025). "Desalination Markets 2025: Global Forecast and Analysis." https://www.globalwaterintel.com
• International Desalination Association. (2024). "IDA Desalination and Water Reuse Handbook." https://idadesal.org
• United Nations Water. (2024). "UN World Water Development Report 2024: Water for Prosperity and Peace." https://www.unwater.org/publications
• Werber, J.R. et al. (2024). "Next-Generation Desalination Membranes: Materials, Performance, and Prospects." Water Research, Volume 254.
• Cambridge University Press. (2025). "Environmental Impacts of Seawater Desalination: Brine Discharge and Marine Ecology." Environmental Reviews.
• Jones, E. et al. (2024). "The state of desalination and brine production: A global outlook." Science of the Total Environment, Volume 912.
• IDE Technologies. (2024). "Sorek B: Advancing the State of the Art in Seawater Desalination." https://www.ide-tech.com