GEF

Unit 4  |  The Global Water Crisis 98 WATER CONCEPTS: DESALINATION As a response to water scarcity, some coastal regions and cities have invested in seawater desalination, a technique for producing fresh water from salt water. The number of desalination plants is growing rapidly, especially in the water-starved Middle East. Several methods of desalination are used. The most common is vacuum distillation, in which seawater is boiled and condensed at low atmospheric pressure, requiring less energy to heat the water. A more energy-efficient approach is reverse osmosis, in which seawater is forced through a fine membrane, trapping salts and allowing fresh water to pass through. Desalination is expensive and requires a lot of energy, so it is usually not an option in less-developed countries where water issues are most pressing. Producing fresh water from salt water also has negative effects on the environment. When seawater is taken from the ocean for desalination, many marine organisms can be killed. Desalination also produces extremely salty wastewater that may contain cleaning chemicals and other toxins. In addition, the energy used to run desalination plants normally comes from burning fossil fuels, contributing to climate change and creating air pollution. Some innovative desalination plants, such as one in Perth, Australia, use wind energy to provide a portion of their power. While desalination is a necessity in some countries that cannot meet their domestic water needs, most sustainability advocates maintain that it is a last resort. Instead, the comprehensive use of water conservation to reduce water waste can often reduce the need to obtain new supplies of fresh water.