Turning seawater into drinking water now takes a tenth of the energy
In 1970, stripping the salt from a cubic metre of seawater took roughly 20 to 30 kilowatt hours of energy. By 2018 the global average had fallen to about 3. That tenfold improvement helps explain why more than 16,800 plants worldwide could, by 2020, produce around 97 million cubic metres of fresh water a day.
The basic trick is old. Aristotle noted that seawater which evaporates condenses as sweet, salt-free water, and claimed to have tested it. For centuries that principle, boiling and collecting the vapour, served mainly on ships, where fresh water decided how long a voyage could last. The Elizabethan seaman Richard Hawkins reported distilling seawater for his crew, and English patents for desalting devices were granted in 1675 and 1683, though neither machine could be scaled up.
Steam engines changed the picture in the nineteenth century, both by demanding pure boiler water and by improving thermal know-how. Multiple-effect evaporators reused heat across several stages, and a simple vertical-tube still, patented by Alphonse René le Mire de Normandy in 1852, was widely adopted at sea. The US Army installed his evaporators at Key West in the 1860s. After 1945 new flash distillation methods spread, and in 1961 a drought-stricken Freeport, Texas, got America's first industrial plant.
The real shift came with reverse osmosis, which forces salty water under pressure through a membrane that holds back the dissolved salts. Sidney Loeb and colleagues at UCLA built pilot systems proving it could supply towns, a commercial plant for brackish water opened in California in 1965, and seawater followed in 1975. It now dominates the industry. The largest single facility, Ras Al-Khair in Saudi Arabia, can deliver over 1.4 million cubic metres daily.
Geography still sets limits. Because water is heavy, a 2005 study reckoned that lifting it 2,000 metres or piping it more than 1,600 kilometres costs as much as desalting it, which is bad news for inland or high cities such as New Delhi or Mexico City. Riyadh drinks desalinated water pumped 320 kilometres from Jubail on the coast. In 2023 Israel even used it to top up the Sea of Galilee.
Source: Desalination
