Desalination is the industrial process of removing salts and minerals from saline water—primarily seawater—to produce potable water suitable for human consumption or agricultural irrigation. As global freshwater scarcity intensifies, these facilities have transitioned from niche emergency installations to critical infrastructure, particularly in the arid coastal regions of the Middle East, North Africa, and the Levant.
Modern desalination is dominated by two distinct physical approaches: thermal distillation and membrane-based separation.
Thermal methods mimic the natural hydrological cycle by inducing a phase change. In Multi-Stage Flash (MSF) distillation, seawater is heated under pressure and then passed through a series of chambers (stages) with successively lower pressures. This causes the water to "flash" into steam instantaneously. The steam is then condensed into pure water, while the remaining concentrated brine is discharged. Multiple-Effect Distillation (MED) employs a similar principle but uses a series of heat exchangers (effects) to reuse the latent heat of vaporization from one stage to heat the next, increasing thermodynamic efficiency.
Reverse Osmosis is currently the fastest-growing technology due to its lower energy requirements. Unlike distillation, RO does not require a phase change. Instead, it utilizes semi-permeable membranes—typically thin-film composites of aromatic polyamide. High-pressure pumps force seawater against these membranes at pressures exceeding the natural osmotic pressure of the brine. This forces water molecules through the microscopic pores of the membrane while rejecting the larger dissolved salt ions.
The energy intensity of desalination is the primary constraint on its deployment. In 2018, the global energy intensity of seawater desalination was approximately $3\text{ kWh/m}^3$, a significant reduction from the $20\text{--}30\text{ kWh/m}^3$ observed in the 1970s. The theoretical minimum energy required for reverse osmosis is approximately $1\text{ kWh/m}^3$.
The scale of these operations is immense. Global capacity has reached roughly $97\text{--}114\text{ million m}^3/\text{day}$. The Ras Al Khair plant in Saudi Arabia stands as a primary example of this scale, with a capacity of $1,401,000\text{ m}^3/\text{day}$.
The physical output of a desalination plant is not merely fresh water, but also a highly concentrated waste stream known as brine. This brine is denser than the surrounding seawater and often contains residual pretreatment chemicals (such as anti-scalants and biocides). When discharged, brine plumes sink to the ocean floor, potentially creating hypoxic zones and disrupting benthic ecosystems.
Despite these costs, desalination provides an absolute water security baseline for nations like Israel, the UAE, and Saudi Arabia, where it is often the only reliable source of water independent of erratic rainfall patterns.