Desalination is the process of removing salt and minerals from seawater or brackish water to produce fresh drinking water. While it works, and over 20,000 plants operate worldwide, it remains expensive, energy-hungry, and environmentally damaging compared to other water sources. Treating seawater through desalination uses up to 10 times more electricity than treating fresh surface water or groundwater, which is the core reason many experts consider it an inefficient solution to water scarcity.
How Desalination Works
There are two main approaches to turning saltwater into fresh water. The most common today is reverse osmosis, which forces seawater through tightly wound membranes under high pressure. The membranes have pores small enough to let water molecules through while blocking dissolved salts. The other approach is thermal desalination, which heats seawater until it evaporates, then collects the steam and condenses it back into liquid, leaving the salt behind. Thermal plants often use multi-stage flash distillation, running water through dozens of chambers at progressively lower pressures so it boils at lower and lower temperatures. One well-studied thermal plant operates 24 stages and heats brine to 110°C.
Reverse osmosis has largely overtaken thermal methods because it requires less energy per unit of water. But both approaches share the same fundamental challenge: separating water from salt takes a lot of energy no matter how you do it, and there’s a hard thermodynamic floor below which you can’t go.
The Energy Problem
Energy consumption is the single biggest factor making desalination inefficient. A typical large-scale seawater reverse osmosis plant consumes roughly 3 to 5 kilowatt-hours of electricity for every cubic meter of drinking water it produces. The most efficient plant in the world, a 2,500 cubic meter per day facility that earned a Guinness World Record in February 2025, achieved 1.794 kWh per cubic meter. That’s impressive for desalination, but still vastly more than conventional water treatment, which can run below 0.5 kWh per cubic meter.
In California, energy costs alone run about $3 to $4 per 1,000 gallons of desalinated water. When the electricity comes from fossil fuels, the carbon footprint adds up fast. Life cycle analyses of seawater reverse osmosis plants show emissions of about 3.26 kg of CO₂ equivalent per cubic meter of water produced. The operational power supply is the dominant carbon source, followed by the chemicals used in the process, membrane manufacturing, and disposal.
Why It Costs So Much More Than Other Water
Desalinated seawater currently costs between $0.80 and $2.50 per cubic meter, depending on the plant’s location, scale, and energy source. That’s several times what utilities pay for treated river water or groundwater. Projections suggest costs could drop to $0.50 to $1.00 per cubic meter by 2030 as technology improves and renewable energy gets cheaper, but even the optimistic end of that range remains more expensive than most conventional freshwater sources.
The high cost isn’t just about electricity. Reverse osmosis membranes have a limited lifespan and are typically replaced every five to seven years. Fouling, where biological growth, mineral scaling, or suspended particles clog the membrane surface, gradually reduces performance and forces more frequent cleaning or early replacement. Used membranes generally end up in landfills. The plant itself requires expensive corrosion-resistant materials because it handles concentrated saltwater under high pressure, and pretreatment systems add another layer of cost and complexity.
Brine Discharge and Marine Ecosystems
For every liter of fresh water a desalination plant produces, it generates a nearly equivalent volume of brine, a concentrated waste stream with roughly twice the salinity of normal seawater. Modern reverse osmosis systems recover about 40 to 50 percent of the intake water as fresh water. The rest goes back to the ocean as hypersaline discharge, often carrying chemical additives like antiscalants and coagulants used during the treatment process.
This brine doesn’t just disappear. Studies of three major desalination facilities along the Israeli coast found that the discharge creates measurable zones of elevated salinity and temperature on the seafloor. At the Ashkelon plant, the disturbed area extended about 1.2 square kilometers, with salinity increases of 2.5 to 9 percent above background levels near the seabed. The Hadera and Sorek plants showed similar footprints, ranging from 0.5 to 1.5 square kilometers of affected seafloor. Research published by the American Chemical Society found that brine and its chemical additives can alter the chemistry of seafloor sediments, changing the conditions that bottom-dwelling organisms depend on.
Some discharge points also showed elevated concentrations of metals like chromium and manganese, though patterns varied between sites. The long-term effects on marine life in these zones are still being studied, but the concern is clear: as the number and size of desalination plants grow, so do the cumulative zones of ecological disruption along coastlines.
Killing Marine Life at the Intake
The damage isn’t limited to what comes out of the plant. What goes in matters too. Surface water intakes, the pipes that pull seawater into the facility, trap and kill marine organisms in two ways. Larger fish and animals get pinned against intake screens (impingement), while eggs, larvae, and plankton are sucked straight through (entrainment). California’s State Water Resources Control Board estimated that open ocean intakes used by the state’s coastal facilities destroy roughly 70 billion fish larvae and other marine organisms every year. The same style of intake is used or proposed for many desalination plants.
Subsurface intakes, which draw water through the sand beneath the seafloor, reduce this problem significantly. But they’re more expensive to build, harder to maintain, and not feasible at every coastal site.
Where Desalination Still Makes Sense
Despite all these drawbacks, desalination is sometimes the only realistic option. Israel now produces a large share of its municipal drinking water through desalination, a necessity in a region with limited natural freshwater. Arid Gulf states, island nations, and drought-stricken coastal cities face similar calculations: the cost and environmental impact of desalination, while real, may be lower than the cost of having no water at all.
The technology is also improving. Pairing desalination plants with solar or wind energy cuts both the carbon footprint and operating costs. New membrane materials resist fouling longer. Some facilities are experimenting with extracting useful minerals from brine rather than dumping it. But these advances narrow the gap rather than close it. Desalination remains a last-resort water source for most of the world, not because the technology doesn’t work, but because the energy, cost, and environmental penalties make nearly every other freshwater option more practical when it’s available.