Areas that have limited surface water or groundwater may choose to desalinate. RO is an increasingly common method, because of its relatively low energy consumption.
Energy consumption is around , with the development of more efficient energy recovery devices and improved membrane materials. According to the International Desalination Association, for 2011, RO was used in 66% of installed desalination capacity (0.0445 of 0.0674 km/day), and nearly all new plants. Other plants use thermal distillation methods: multiple-effect distillation, and multi-stage flash.
Sea-water RO (SWRO) desalination requires around 3 kWh/m, much higher than those required for other forms of water supply, including RO treatment of wastewater, at 0.1 to 1 kWh/m. Up to 50% of the seawater input can be recovered as fresh water, though lower recovery rates may reduce membrane fouling and energy consumption.
Brackish water reverse osmosis (BWRO) is the desalination of water with less salt than seawater, usually from river estuaries or saline wells. The process is substantially the same as SWRO, but requires lower pressures and less energy. Up to 80% of the feed water input can be recovered as fresh water, depending on feed salinity.
The Ashkelon desalination plant in Israel is the world's largest.
The typical single-pass SWRO system consists of:
* Intake
* Pretreatment
* High-pressure pump (if not combined with energy recovery)
* Membrane assembly
* Energy recovery (if used)
* Remineralisation and pH adjustment
* Disinfection
* Alarm/control panel