How Does Desalination Work?

With freshwater scarcity affecting over 2 billion people, desalination has become critical infrastructure. Reverse osmosis (RO), the dominant technology (about 69% of global capacity), works by pumping seawater at 50-80 bar of pressure through semi-permeable membranes that allow water molecules to pass but block dissolved salts. Modern RO membranes reject over 99.5% of dissolved salts. Multi-stage flash (MSF) distillation, the second most common method, heats seawater and evaporates it through a series of chambers at progressively lower pressures — each "flash" produces more vapour. The vapour condenses as fresh water. Desalination is energy-intensive: RO requires about 3-4 kWh per cubic metre (down from 20+ kWh in the 1970s thanks to energy recovery devices). Saudi Arabia and the UAE are the largest producers, and Israel now gets about 80% of its domestic water from desalination. The Ras Al Khair plant in Saudi Arabia is the world largest, producing over 1 million cubic metres per day.