Desalination

http://en.wikipedia.org/wiki/Desalination

Desalination, desalinization, and desalinisation refer to any of several processes that remove some amount of salt and other minerals from saline water. More generally, desalination may also refer to the removal of salts and minerals, as in soil desalination.

Salt water is desalinated to produce fresh water suitable for human consumption or irrigation.

Due to relatively high energy consumption the cost of desalinating sea water are generally higher than the alternatives (fresh water from rivers or groundwater, water recycling and water conservation), but alternatives are not always available.

Methods

vacuum distillation

The traditional process used in these operations is vacuum distillation—essentially the boiling of water at less than atmospheric pressure and thus a much lower temperature than normal. This is because the boiling of a liquid occurs when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature. Thus, because of the reduced temperature, low-temperature "waste" heat from electrical power generation or industrial processes can be used.

reverse osmosis

The principal competing processes use membranes to desalinate, principally applying reverse osmosis technology.^[8]Membrane processes use semipermeable membranes and pressure to separate salts from water. Reverse osmosis plantmembrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade.

Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.