Desalination converts salty water into drinkable water by removing salt and other solids from seawater or brackish water. Although the desalination process has been around for centuries, desalination plants allowing large-scale treatment of water didn't come into being until the 1950s. In 2002, 12,500 desalination plants in 120 countries provided 14 million cubic meters per day of fresh drinking water. Worldwide desalination plant capacity will nearly double by 2015, according to the market research firm Global Water Intelligence.
Advantage: Provides accessible drinking water
Desalination plants can provide drinking water in areas where no natural supply of potable water exists. Some Caribbean islands get almost all of their drinking water through desalination plants, and Saudi Arabia gets 70 per cent of its fresh water via the process. Even in countries where fresh water is plentiful, desalination plants can provide water to drier areas or in times of drought. The United States, for example, uses 6.5 per cent of the world's supply of desalinated water.
Disadvantage: High costs to build and operate
It is very costly to build and operate desalination plants. Depending on their location, building a plant can cost from £195 million to £1.9 billion as of 2008. Once operational, plants require huge amounts of energy. Energy costs account for one-third to one-half of the total cost of producing desalinated water. Because energy is such a large portion of the total cost, the cost is also greatly affected by changes in the price of energy. The California Coast Commission estimated that a one cent increase in the cost of a kilowatt-hour of energy raises the cost of one acre-foot of desalinated water by £32.
Advantage: Quality and habitat protection
Desalinised water generally meets or exceeds standards for water quality. Desalination plants can also reduce pressure on freshwater supplies that come from areas that need protecting. By treating ocean water rather than removing water from sources that may also be habitats for endangered species, these important freshwater bodies can be preserved. In addition, the California Coastal Commission states that "[t]he perception of the ocean as a source of water supply may result in increased public awareness and protection of oceans."
Disadvantage: Environmental impact
Environmental impacts are another disadvantage to desalination plants. Disposal of the salt removed from the water is a major issue. This discharge, known as brine, can change the salinity and lower the amount of oxygen in the water at the disposal site, stressing or killing animals not used to the higher levels of salt. In addition, the desalination process uses or produces numerous chemicals including chlorine, carbon dioxide, hydrochloric acid and anti-scalents that can be harmful in high concentrations.