Desalination is the process of removing dissolved salts from water. The two most common desalination technologies are thermal and membrane technologies. The thermal process involves heating saline water to produce water vapor which is then condensed and collected as fresh water. Membrane processes rely on semi-permeable membranes to separate salts from water. Membrane processes can be pressure-driven (reverse osmosis or RO, the most common method used in desalination), or voltage-driven (electrodialysis and electrodialysis reversal).