What is the process that removes salt from sea water?

The process that removes salt from sea water is desalination. It converts salt water, usually seawater, into fresher water by separating dissolved salts and other minerals from the water.

Modern desalination mainly uses reverse osmosis or thermal distillation. Reverse osmosis forces seawater through a semipermeable membrane that blocks most salts, while distillation boils water and condenses the vapor, leaving salt behind. Both methods produce fresh water and a concentrated salty by-product called brine.

Desalination is especially important in dry coastal regions, including parts of the Middle East, North Africa, Australia, Spain, and California. It is not the same as ordinary water filtration: most household filters remove particles or particular contaminants but do not remove the dissolved sodium chloride that makes seawater salty.

The technology has ancient roots in the idea of evaporating and re-condensing seawater, but large modern plants became practical with advances in membranes, pumps, and energy systems. Desalinated water can support drinking supplies and irrigation, although energy use, cost, and brine disposal remain major challenges.