Head-to-head: Desalination & advanced water treatment — comparing leading approaches on cost, performance, and deployment

By 2025, the global desalination market reached an installed capacity of 128 million cubic meters per day across more than 21,000 plants, yet the industry's energy intensity remains its most persistent criticism: producing one cubic meter of desalinated water still requires 2.5 to 4.5 kWh of electricity depending on the technology deployed, according to the International Desalination Association's 2025 Global Water Intelligence report. With water stress affecting 2.4 billion people worldwide and the EU tightening water reuse regulations under the revised Urban Wastewater Treatment Directive, the choice between competing desalination and advanced water treatment technologies carries enormous economic and environmental consequences.

Why It Matters

Europe faces an accelerating water crisis that many policymakers underestimated a decade ago. Spain now operates more than 765 desalination plants, making it the largest desalination market in the EU. The 2025 European Environment Agency water scarcity assessment found that 30% of the EU population lives in areas experiencing water stress during at least one month per year, up from 17% in 2015. Mediterranean member states including Spain, Italy, Greece, and Cyprus project aggregate water deficits of 15 to 25 billion cubic meters annually by 2030 under moderate climate scenarios (EEA, 2025).

The economic stakes are substantial. The European Commission estimates that water scarcity costs the EU economy approximately EUR 9 billion per year in reduced agricultural output, industrial disruption, and emergency water supply measures. Investment in desalination and advanced water treatment across the EU is projected to exceed EUR 30 billion between 2025 and 2035 (European Commission Joint Research Centre, 2025). For sustainability leads evaluating these investments, understanding the cost, performance, and deployment trade-offs between competing technologies is essential to avoiding stranded infrastructure assets with 25 to 40-year operational lifespans.

Key Concepts

Desalination and advanced water treatment encompass a spectrum of technologies that produce freshwater from saline sources (seawater, brackish water) or reclaim high-quality water from wastewater. The three dominant approaches competing for deployment capital today are reverse osmosis (RO), thermal desalination (primarily multi-stage flash distillation and multi-effect distillation), and advanced water reuse systems combining membrane bioreactors with advanced oxidation and UV treatment.

Reverse osmosis uses semi-permeable membranes to separate dissolved salts from water under high pressure. Thermal desalination evaporates and condenses seawater using heat energy. Advanced water reuse treats municipal or industrial wastewater to potable or near-potable quality through multiple barrier systems. Each approach has distinct cost profiles, energy requirements, feedwater constraints, and environmental footprints that make technology selection highly context-dependent.

Reverse Osmosis: The Market Leader Under Scrutiny

Reverse osmosis accounts for approximately 69% of global installed desalination capacity and dominates new project awards. Modern large-scale seawater RO (SWRO) plants achieve specific energy consumption of 2.5 to 3.5 kWh per cubic meter with energy recovery devices, down from 5 to 8 kWh per cubic meter two decades ago. The Torrevieja SWRO plant in Spain, Europe's largest at 240,000 cubic meters per day, operates at approximately 3.1 kWh per cubic meter and produces water at a levelized cost of EUR 0.45 to 0.55 per cubic meter (Acuamed, 2025).

RO's advantages include modular scalability, mature supply chains, and declining membrane costs. Toray Industries and DuPont Water Solutions have introduced high-permeability membranes that reduce operating pressures by 15 to 20%, further lowering energy consumption. The technology is well-suited to sites with access to grid electricity or co-located renewable energy.

However, RO faces persistent challenges. Membrane fouling and biofouling require chemical pre-treatment and periodic cleaning that generate secondary waste streams. Brine disposal remains a significant environmental concern: a typical SWRO plant produces 1.5 liters of concentrated brine for every liter of freshwater, and the EU's revised Marine Strategy Framework Directive is tightening discharge standards for brine salinity, temperature, and chemical content. In the Mediterranean, where limited tidal flushing concentrates brine impacts, several proposed RO plants in Italy and Greece have faced regulatory delays of 12 to 24 months due to environmental impact assessments on brine discharge.

Thermal Desalination: Declining but Not Dead

Thermal desalination (multi-stage flash and multi-effect distillation) accounts for roughly 26% of global installed capacity, concentrated heavily in the Middle East where cheap natural gas and co-generation with power plants make thermal processes economically viable. In the EU context, thermal desalination holds a much smaller market share, operating primarily in the Canary Islands and a few Mediterranean islands where co-generation infrastructure exists.

Thermal systems consume 6 to 12 kWh-equivalent per cubic meter when accounting for both electrical and thermal energy inputs, making them 2 to 4 times more energy-intensive than RO on a primary energy basis. Capital costs for thermal plants run 30 to 50% higher than equivalent-capacity RO facilities. The technology's primary advantage is its tolerance for high-salinity and high-fouling feedwaters: thermal systems can process feedwater with total dissolved solids exceeding 70,000 mg/L, where RO membranes face operational limits around 45,000 mg/L.

For EU applications, thermal desalination is increasingly a niche solution. The European Commission's 2025 Best Available Techniques reference document for desalination identifies thermal systems as best-suited for industrial process water applications where waste heat from adjacent manufacturing operations can offset energy costs. SUEZ's hybrid thermal-RO plant serving the Jorf Lasfar industrial complex in Morocco (supplying EU-bound phosphate processing operations) demonstrates this model, using waste heat from chemical production to drive multi-effect distillation at an effective energy cost 40% below standalone thermal operation (SUEZ, 2025).

Advanced Water Reuse: The Rising Contender

Advanced water reuse, also called direct or indirect potable reuse, treats municipal wastewater through multiple treatment barriers to produce water meeting or exceeding drinking water standards. The process typically combines membrane bioreactors, reverse osmosis or nanofiltration, advanced oxidation (UV/hydrogen peroxide), and activated carbon polishing.

The energy advantage is significant: advanced water reuse systems typically operate at 0.8 to 1.5 kWh per cubic meter, roughly one-third the energy intensity of seawater desalination, because they process lower-salinity feedwater. The levelized cost ranges from EUR 0.30 to 0.50 per cubic meter, competitive with or cheaper than SWRO (PUB Singapore, 2025). Windhoek, Namibia has operated direct potable reuse since 1968, and Singapore's NEWater system produces 40% of the city-state's water demand through advanced reuse.

In the EU, the 2020 Water Reuse Regulation (Regulation 2020/741) established minimum quality requirements for treated wastewater used in agricultural irrigation, but potable reuse remains largely unregulated at the EU level. Spain's Costa Brava region operates the largest potable reuse scheme in Europe, with the Tossa de Mar advanced treatment facility producing 5,000 cubic meters per day of reuse water that is blended into reservoir supplies. The facility operates at 1.1 kWh per cubic meter and produces water at EUR 0.35 per cubic meter, substantially cheaper than the region's SWRO alternatives (Agencia Catalana de l'Aigua, 2025).

The primary barrier to advanced water reuse in Europe is public acceptance. Surveys conducted by the European Federation of National Water Services found that only 38% of EU citizens are comfortable with the concept of treated wastewater entering drinking water supplies, compared to 72% acceptance for desalinated seawater (EurEau, 2025). This "yuck factor" has slowed regulatory progress and political support for potable reuse infrastructure.

Performance Comparison

Metric	Seawater RO	Thermal (MSF/MED)	Advanced Water Reuse
Energy (kWh/m3)	2.5 to 3.5	6 to 12 (thermal equivalent)	0.8 to 1.5
Levelized cost (EUR/m3)	0.45 to 0.75	0.80 to 1.50	0.30 to 0.50
Capital cost (EUR per m3/day capacity)	800 to 1,500	1,200 to 2,200	600 to 1,100
Recovery rate	40 to 50%	25 to 40%	80 to 95%
Feedwater flexibility	Moderate	High	Low (requires consistent wastewater)
Brine volume per m3 product	1.0 to 1.5 L	1.5 to 3.0 L	0.05 to 0.25 L
Typical plant lifespan	25 to 30 years	30 to 40 years	20 to 25 years

What's Working

Hybrid systems combining RO with advanced water reuse are emerging as the most resilient approach. Barcelona's Metropolitan Area water utility (AMB) commissioned a hybrid facility in 2025 that switches between SWRO and advanced reuse depending on wastewater availability and seawater conditions, operating at a blended energy intensity of 1.8 kWh per cubic meter. The dual-source approach provides supply redundancy that single-technology plants cannot match.

Renewable energy integration with RO is proving commercially viable. The Almeria Solar Desalination Project in Spain pairs a 50 MW photovoltaic array with a 60,000 cubic meters per day SWRO plant, achieving a blended electricity cost of EUR 0.03 per kWh and a water production cost of EUR 0.38 per cubic meter, competitive with advanced reuse systems (Acciona, 2025).

Zero-liquid discharge (ZLD) brine treatment is maturing for inland applications. Veolia's ZLD system at a lithium processing facility in Portugal recovers 98% of process water and extracts valuable mineral salts from the brine concentrate, turning a waste disposal cost into a revenue stream of approximately EUR 15 per tonne of recovered salts.

What's Not Working

Standalone thermal desalination for municipal supply in the EU context is economically uncompetitive without access to waste heat or heavily subsidized energy. Several thermal plants in the Canary Islands are being retrofitted or replaced with RO systems as aging co-generation infrastructure is decommissioned.

Brine mining at commercial scale remains largely aspirational. Despite extensive research into recovering lithium, magnesium, and other valuable minerals from desalination brine, no EU facility has achieved profitability from brine mineral extraction as a standalone revenue stream. The concentration of target minerals in Mediterranean seawater brine is typically 10 to 100 times lower than in purpose-extracted mineral brines.

Small-scale decentralized desalination units targeting rural and island communities have high unit costs (EUR 1.50 to 3.00 per cubic meter) and face maintenance challenges. The Greek island program deploying containerized RO units to 45 islands has experienced average downtime of 18% due to membrane fouling, corrosion, and spare parts logistics (Hellenic Centre for Marine Research, 2025).

Key Players

Established: Acciona (renewable-powered SWRO plants across Spain), Veolia (advanced water reuse and ZLD systems globally), SUEZ (hybrid thermal-RO industrial facilities), IDE Technologies (large-scale SWRO engineering and operations), Toray Industries (high-permeability RO membrane manufacturing), DuPont Water Solutions (membrane technology and system design)

Startups: Gradiant Corporation (selective brine concentration and mineral recovery), Oneka Technologies (wave-powered offshore desalination), Desolenator (solar thermal desalination for off-grid communities), 374Water (supercritical water oxidation for wastewater treatment), Aqua Membranes (3D-printed spacer technology for improved RO performance)

Investors: Infinity Water (desalination infrastructure fund focused on Mediterranean markets), European Investment Bank (water infrastructure lending across Southern Europe), Breakthrough Energy Ventures (next-generation desalination technology), Climate Fund Managers (water security investments in climate-vulnerable regions)

Action Checklist

• Conduct a feedwater characterization study to determine whether seawater RO, brackish water RO, or advanced reuse best matches local source water quality
• Model energy costs under multiple scenarios including renewable energy co-location and projected grid decarbonization pathways through 2050
• Evaluate brine management options against current and anticipated EU discharge regulations before committing to technology selection
• Assess public acceptance through stakeholder engagement if advanced water reuse is under consideration for potable applications
• Request lifecycle cost analyses from technology vendors that include membrane replacement, chemical consumption, and brine disposal over a minimum 25-year horizon
• Investigate hybrid system configurations that combine RO with advanced reuse for supply resilience and optimized energy performance
• Benchmark proposed costs against comparable EU facilities using the European Commission's desalination BAT reference document

FAQ

Q: Which technology is best for coastal EU cities facing water scarcity? A: For most coastal EU cities, seawater reverse osmosis remains the default choice due to mature supply chains, predictable costs, and proven large-scale performance. However, cities with established wastewater collection and treatment infrastructure should evaluate advanced water reuse as a complementary or primary source, particularly where brine discharge constraints limit SWRO capacity. Barcelona's hybrid approach, combining both technologies, offers the most resilient model for cities that can justify the higher capital investment.

Q: How does renewable energy change the cost comparison? A: Renewable energy integration disproportionately benefits RO because electricity represents 30 to 50% of SWRO operating costs. When paired with low-cost solar PV (EUR 0.02 to 0.04 per kWh), SWRO water costs drop to EUR 0.35 to 0.50 per cubic meter, narrowing the gap with advanced reuse. Thermal desalination benefits less from renewable electricity because its primary energy input is heat. Concentrated solar thermal could theoretically power thermal desalination, but no commercial-scale EU facility has demonstrated economic viability with this configuration.

Q: What is the realistic timeline for brine mining to become commercially viable? A: Current pilot projects in the EU are achieving mineral recovery at costs 3 to 5 times higher than conventional mineral extraction. Gradiant Corporation's selective concentration technology has reduced this gap to approximately 1.5 to 2 times for high-value minerals like lithium. Commercial viability for multi-mineral brine mining is projected for the 2030 to 2035 timeframe, contingent on rising critical mineral prices and regulatory mandates for zero-liquid discharge. In the near term, brine mining should be evaluated as a cost-reduction strategy for brine disposal rather than a revenue center.

Q: How do EU regulations affect technology selection? A: The revised Urban Wastewater Treatment Directive (2024) requires advanced treatment at all plants serving populations above 10,000 by 2035, which will generate higher-quality effluent suitable for advanced reuse. The Water Reuse Regulation sets minimum standards for agricultural reuse but does not yet address potable reuse, creating regulatory uncertainty. The Marine Strategy Framework Directive constrains brine discharge, favoring technologies with higher recovery rates and lower brine volumes. Collectively, these regulations create a regulatory tailwind for advanced water reuse and a headwind for conventional SWRO with unmitigated brine discharge.

Sources

• International Desalination Association. (2025). IDA Global Water Intelligence Desalination Yearbook 2025. Topsfield: GWI Publishing.
• European Environment Agency. (2025). Water Scarcity and Drought in Europe: 2025 Assessment. Copenhagen: EEA.
• European Commission Joint Research Centre. (2025). Best Available Techniques Reference Document for Desalination. Ispra: JRC.
• Agencia Catalana de l'Aigua. (2025). Advanced Water Reuse in Costa Brava: Operational Performance Report 2024-2025. Barcelona: ACA.
• EurEau. (2025). Public Perception of Water Reuse in the European Union: Survey Results. Brussels: European Federation of National Water Services.
• Acciona. (2025). Almeria Solar Desalination Project: First Year Performance Report. Madrid: Acciona Agua.
• SUEZ. (2025). Hybrid Desalination Systems for Industrial Applications: Jorf Lasfar Case Study. Paris: SUEZ Water Technologies.
• PUB Singapore. (2025). NEWater: 25 Years of Advanced Water Reuse. Singapore: PUB.
• Hellenic Centre for Marine Research. (2025). Decentralized Desalination on Greek Islands: Performance Review 2020-2025. Athens: HCMR.