Desalination & Water Recycling

The search for water to support large-scale agribusiness has pushed freshwater to its limit. Aquifers such as the Ogallala in the US, the Arabian aquifer in Saudi Arabia, and Sidi Bel Abbes in Algeria are all on the verge of drying up. Large rivers — the Nile, the Fuerte in Mexico, the Yellow River, the Rio Grande — now frequently run dry before reaching the sea, or have their flow severely reduced by dams.

Domestically, we are using more water than ever. On average, every American uses 1,100 liters of water daily, and little of it is ever reused. Nascent water recycling efforts (also called reclamation) yield around 3.4 billion liters per day — about 10 liters per person, and that figure includes recycled industrial wastewater. The amount of recycled domestic water is smaller still: no more than 0.91% of what’s consumed.

There’s also a persistent public trust problem. In 2021, a water treatment plant in Oldsmar, Florida was the victim of a cyberattack in which hackers altered chemical levels, briefly making the water unsafe to drink. Incidents like this harden public opinion against recycled water generally. In Australia, public opposition has repeatedly defeated recycling projects — in 2011, residents outside Brisbane voted down a treatment plant even as the local dam sat at 11% capacity during a severe drought.

More than 50 years since Norman Borlaug’s Nobel-winning work made intensive farming viable, his methods have pushed cultivation into the most marginal land — Arabian, Egyptian, and Mexican deserts — sustained by groundwater and rivers. That grain matters more than ever as the population climbs while soil pollution, climate change, and urban expansion shrink the arable land available. ^[1]

Abandoning marginal farmland once its water runs out isn’t a realistic option, which raises the question this briefing considers: could desalination realistically replace aquifers, rivers, and freshwater lakes as an irrigation source at scale?

Desalination is the process of removing salt and other minerals from seawater so it becomes safe for domestic use and irrigation.^[2] On paper it’s an elegant answer — the planet is 70% water. In practice, transport and purification costs mean only a small fraction of global water supply comes from desalination. Its heaviest use is concentrated in the Mediterranean basin and the Middle East.^[3]

There are three broad approaches. Thermal distillation heats seawater — using solar or conventional energy — to capture and condense vapor, and works best on highly saline or industrial water. Membrane distillation forces seawater through a membrane to strip out salt and minerals, and is well suited to producing water for domestic consumption. Some plants are hybrid, combining both systems.^[4] Desalination can also be scaled up or down depending on need, energy availability, and terrain.

Thermal distillation is the most widely used desalination method, with three main variants: multistage flash distillation, multi-effect distillation, and vapor compression. On average, a thermal plant uses 10–15 kWh to produce 1,000 liters of desalinated water.^[5] More advanced plants recover some of that cost by placing turbines at the seawater intake. Because of this energy appetite, thermal desalination thrives where energy is cheap — which is why Middle Eastern nations with large fossil fuel reserves have invested in it heavily.

Multistage flash distillation

This process uses as many as 30 stages to progressively strip salt from seawater, lowering ambient pressure at each step while managing heat through countercurrent exchange. It’s one of the oldest desalination methods and among the most productive — some plants output around 800 million liters per day^[6] — but the plant and energy costs are steep.

Multi-effect distillation

Multi-effect distillation uses a series of “effects” to heat and evaporate water in stages, reusing heat from the previous stage each time. Because only the first cell needs external heating — later cells run at progressively lower temperature and pressure — the process can use as little as a third of the energy multistage flash distillation requires for the same output, and can run for long stretches with minimal supervision.

Evaporators

Vapor compression and mechanical vapor compression systems raise pressure on produced vapor, releasing heat that’s fed back to warm incoming seawater. They’re rarely used today: energy consumption can run up to three times other thermal methods, and they scale poorly when demand is high.

Membrane processes push seawater through a semipermeable membrane to strip out salt and impurities. The two dominant methods are reverse osmosis and electrodialysis.

Reverse osmosis

Ordinary osmosis moves water from a low-concentration solution to a high-concentration one through a membrane. Reverse osmosis inverts this by applying pressure higher than seawater’s natural osmotic pressure — roughly 55–82 bar — forcing water molecules the “wrong” way and leaving low-salinity water on the other side. It’s favored because it uses meaningfully less power than thermal methods while still scaling to high output.

Electrodialysis

Electrodialysis works in two stages: seawater is electrolyzed while a selective membrane — permeable to either anions or cations, but never both — separates fresh water from the concentrated brine.

The single biggest obstacle to desalination is energy.^[7] Countries with little fresh water but abundant fossil fuel reserves can lean into desalination easily; countries with neither cheap energy nor fresh water are stuck.

A German technology called capacitive deionization — using electrodes to pull ions directly out of water^[8] — is one of the more promising ways out of this bind. Extracted ions are returned to brine water in a step called “desorption,” which regenerates the carbon electrodes. Still early-stage, but if it matures, it could in principle turn desalination from a net energy consumer into a net producer.

Nuclear power has been paired with some desalination plants, supplying cheap heat and electricity to both thermal and membrane systems, though political resistance to nuclear limits its use. Solar desalination exists too, but most solar plants remain small and hard to scale. Other designs nest a low-temperature desalination unit inside a power plant, using waste heat and condensing water at lower temperatures without mechanical pumping or cooling — at the cost of much lower output.

Desalination is energy-hungry and usually fossil-fuel-powered, so its greenhouse gas footprint can be significant at scale. Seawater intakes also pose a direct threat to marine life: California’s desalination plants alone are linked to the deaths of more than 70 billion fish larvae, with real consequences for state fisheries. Well-designed inlets that keep marine life out of the intake stream are essential.

Some environmental groups have proposed using desalination wastewater to help replenish aquifers, discharging it into wells where soil and rock naturally filter out salt — potentially recharging aquifers faster than natural processes alone.

Mitigation

The concentrated brine byproduct needs careful disposal;^[9] its temperature and salinity are hostile to marine life, and diffusers help limit the damage. In most processes, every liter of clean water produced generates 1.5 liters of chlorine- and copper-contaminated waste liquid,^[10] which depletes oxygen and threatens species that coastal communities rely on for food. Transport and further treatment after desalination add still more energy and environmental cost.

Only 1% of Earth’s water is readily drinkable; the rest is seawater or brackish. Desalination has existed at industrial scale for more than 70 years — so why does it remain confined to a handful of water-insecure, energy-rich countries?

Transport

Desalinated water still has to reach the people who need it, typically via pipeline. China, South Africa, and the US all show it’s technically possible to move water across vast distances — China’s South-to-North project alone spans 11 provinces and will displace hundreds of thousands of people, with cultural and ecological costs largely left out of the public conversation. In the US, comparable proposals to move water from the Great Lakes region west have been stopped by residents and a government structure that takes those objections seriously.

Scalability

A single plant on the scale of Ras al Khair costs around $7.2 billion; 200 such plants would run past $1.5 trillion. That kind of spend demands scrutiny — much of Nebraska’s corn, for instance, goes to animal feed, corn syrup, and ethanol, which raises real questions about whether that’s the best use of such an investment. Larger desalination plants also tend to become less efficient per unit of land and energy, which works against scaling this approach elsewhere without an existential trigger, like towns running out of water outright.

Examples: going small

Scalability pressure may ease as the technology shrinks. Hall Labs is developing small desalination devices using multi-effect distillation to treat grey and black water and convert seawater for household use. Paired with better irrigation efficiency and captured runoff, small-scale desalination could eventually serve individual households, communities, or farms directly — while recycling water for both domestic and irrigation use at once.

Large-scale desalinated water for agriculture is an idea whose time hasn’t fully arrived — but it’s coming. As the Ogallala keeps drying and Chinese groundwater recedes roughly 3 meters a year, farmers are increasingly confronting how temporary their current water sources really are. Desalination carries capital, operational, and environmental costs that still need solving before it becomes a mainstream water source.

Regions like Nebraska and the wider Great Plains, once open pasture, are now central to feeding the world — and will likely stay that way unless farming finds a way to produce far more from far less land. Wherever that water ultimately comes from, the question of how to get it there remains unresolved. Future briefings will look at harvesting stormwater for irrigation and the feasibility of long-distance water transport for water-stressed farms.