How ocean water becomes drinking water — the technology, the economics, the environmental tradeoffs, and where it's heading. Everything we've gathered in one place.
Freshwater scarcity is one of the defining infrastructure problems of the century — desalination is the main lever countries with ocean access can pull to manufacture new supply rather than fight over existing supply.
Seawater is forced under high pressure through a semi-permeable membrane that blocks salt ions and other dissolved solids, leaving fresh water on one side and concentrated brine on the other. RO uses mechanical pressure rather than heat, which makes it far more energy-efficient than thermal distillation — the reason it now dominates new plant construction worldwide.
An older thermal method still common across the Gulf. Seawater is heated, then passed through a series of chambers at progressively lower pressure — at each stage some of the water "flashes" instantly into steam, which is then condensed into fresh water. Robust and simple, but energy-hungry compared to RO.
Similar principle to MSF, but each evaporation stage ("effect") reuses the latent heat released by the previous stage to boil the next — meaningfully more thermally efficient than MSF, and often paired with power plants to use waste heat.
Uses an electric field and ion-selective membranes to pull charged salt ions out of the water, rather than pushing water through a membrane. More efficient for brackish (lower-salinity) water than seawater, so it's used more in inland/groundwater desalination than ocean plants.
Emerging methods that use a natural osmotic gradient or a vapor-pressure gradient across a membrane instead of high-pressure pumps. Promising for lower energy use, but still mostly in pilot/development stage — not yet displacing RO at commercial scale.
The single biggest reason RO became commercially viable at scale. ERDs capture the pressure energy still held in the leftover brine stream and transfer it back into incoming seawater — recovering up to ~70% of energy that would otherwise be wasted. Since the 1990s, ERDs have cut seawater RO energy use by up to 60%, taking energy consumption down to roughly 2.5–3 kWh per cubic meter.
Modern large RO plants with energy recovery produce water for roughly $0.40–$0.80 per cubic meter. Saudi Arabia's newest projects hit around $0.50/m³, helped by cheap solar power and fossil-fuel subsidies. Dubai's Hassyan RO plant targeted a record $0.31/m³. Powering the high-pressure pumps is consistently the largest single operating cost — 35–45% of OPEX.
Typical capex runs $1,000–$2,500 per m³/day of daily capacity for seawater RO plants. Scale matters a lot: plants over 100,000 m³/day are 25–40% cheaper per unit than small plants, and true megaplants (over 500,000 m³/day) push that further down.
The global desalination equipment market is valued around $20.8B in 2026, projected to reach $38–59B by 2032–2034 (roughly 9% CAGR). The narrower "desalination technologies" market alone was $27.8B in 2025, heading toward $59.34B by 2034.
Ras Al Khair, Saudi Arabia — built and owned by SWCC (Saline Water Conversion Corporation), producing roughly 3 million m³/day at a project cost of about $7.2 billion. Notable runners-up: Fujairah F1 (~$650–700M) and Fujairah F2 (~$2.17B), both in the UAE, together adding ~230 MIGD of capacity.
SWCC (Saudi Arabia, government-owned) produces about 4.6 million m³/day nationally. Abengoa operates roughly 4.4 million m³/day of global capacity. IDE Technologies supplies about 70% of Israel's potable water, with its largest plant near Tel Aviv producing over 165 million gallons/day. Wabag delivers about 1 million m³/day to over 3.5 million people worldwide. Other major players: Veolia, Suez International, Doosan Enerbility, Acciona, and Fisia Italimpianti.
Saudi Arabia, UAE, Israel, and Spain lead in installed capacity; Australia built major capacity after its 2000s drought; California and India are the fastest-growing newer adopters as groundwater and reservoir supplies come under strain.
Every liter of fresh water produced leaves behind a liter or more of concentrated brine — roughly double the salinity of normal seawater, often mixed with pre-treatment chemicals. Because it's denser than seawater, brine sinks and can creep along the seafloor for several kilometers from the outfall — some modeling shows measurable effects tens of kilometers out, disrupting nutrient exchange between sediment and open water.
Elevated salinity disrupts the osmotic balance of marine organisms, causing cellular dehydration and reduced turgor pressure — in some cases fatal to sensitive species near the discharge zone. This is the most-cited environmental objection to seawater desalination.
Where RO plants still run on fossil-fuel grid power, the energy demand (2.5–3+ kWh/m³ even with ERDs) carries a real carbon footprint — one reason the pairing of desalination with solar power (as in Saudi Arabia's newest builds) is a major cost and emissions story.
Instead of dumping brine back into the ocean, ZLD systems process it further to extract valuable minerals — sodium, magnesium, calcium, potassium, lithium, strontium, bromine, boron, iodine, and even uranium are all present in desalination brine. Recovering them turns a waste-disposal liability into a secondary revenue stream while cutting the discharge volume that would otherwise hit marine ecosystems.
Advanced RO membranes now achieve salt rejection above 99.7%. Graphene-oxide membranes in development promise even better rejection at lower energy cost — the long-rumored "holy grail" material for this field.
New passive solar desalination designs (covered by ScienceDaily in May 2026) produce fresh water without generating toxic brine waste at all — a fundamentally different architecture from RO, aimed at small-scale/off-grid deployment rather than megaplants.
Machine learning models now run in real time on plant operations — detecting membrane fouling before it causes a shutdown, and continuously tuning energy use against changing seawater conditions.
Pairing RO plants directly with solar and wind generation (rather than grid power) is becoming standard for new builds in sunny, water-stressed regions — directly attacking both the cost and emissions problems at once.