Desalinization is removal of salt and other chemicals from the sea water to create potable water. Though today a number of technologies are used for desalinization, this process of salt removal has been practiced since ancient times.
Why should I be aware of this?
Though three quarters of the Earth's surface is covered with water, most of it is too salty to drink. Of the only 2.5 percent that is freshwater, most is locked up either in soil, remote snowpacks and glaciers or in deep aquifers. That leaves less than 1 percent of all freshwater for humans and animals to drink and for farmers to use to raise crop.
Even this very small percentage is shrinking because of rising global warming. As the world population grows, it is becoming increasingly difficult to meet the needs for water.
All about desalization
Extensive desalinization could not be taken up because of high costs. But that's changing as technology improves and growing demand is putting pressure on freshwater supplies.
The two main desalinization techniques are distillation and reverse osmosis (RO). In distillation technique, in which the raw water is evaporated and then condensed as freshwater, is energy-intensive. This technique is mainly used in the Middle East where there is abundant oil.
Thermal salt-removing processes is expensive because it requires high temperatures. But by using rejected "waste" heat from other industrial or power plant operations for co-generation energy expenditure can be reduced.
RO, which is based on high-tech polymer membranes that are permeable to water, is more commonly used in desalinization plants. When a saline solution sits on one side of a semipermeable membrane and a less salty solution is on the other, water diffuses through the membrane from the less concentrated to the more concentrated side. Scientists call this phenomenon osmosis, which tends to equalize the salinity of the two solutions.
During World War II small solar stills were developed for desalinating sea water. These devices imitate the natural hydrologic cycle in that the sun's rays heat the sea water so that the production of water vapor (humidification) increases. The water vapor is then condensed on a cool surface, and the condensate collected as fresh water.
Although the thermal energy may be free, the stills are expensive to construct. Additional energy is needed to pump the water to and from the facility. Vapor can leak from the stills, and careful operation and maintenance is needed to prevent scale formation. Generally, these types of solar humidification units have been used for desalinating sea water on a small scale, where solar energy is abundant but electricity is not.
Extensive work was done in the 1950s and 1960s to develop freezing desalinization. During the process of freezing, dissolved salts are naturally excluded from the lattice structure of ice crystals. Cooling the water to form ice under controlled conditions can desalinate sea water. Before the entire mass of water has been frozen, the ice is removed and rinsed to remove any salts adhering to the ice surface. It is then melted to produce fresh water.
- Desalination/Distillation is one of mankind's earliest forms of water treatment, and it is still a popular treatment solution throughout the world today. 
- In ancient times, many civilizations used this process on their ships to convert sea water into drinking water. 
- Today, desalination plants are used to convert sea water to drinking water on ships and in many arid regions of the world, and to treat water in other areas that is fouled by natural and unnatural contaminants. 
- Distillation is perhaps the one water treatment technology that most completely reduces the widest range of drinking water contaminants. 
- It is estimated that some 30% of the world’s irrigated areas suffers from salinity problems and remediation is seen to be very costly. 
- In 2002 there were about 12,500 desalination plants around the world in 120 countries. They produce some 14 million m³/day of freshwater, which is less than 1% of total world consumption. 
- The most important users of desalinated water are in the Middle East, (mainly Saudi Arabia, Kuwait, the United Arab Emirates, Qatar and Bahrain), which uses about 70% of worldwide capacity; and in North Africa (mainly Libya and Algeria), which uses about 6% of worldwide capacity. 
- Among industrialized countries, the United States is one of the most important users of desalinated water (6.5%), specially in California and parts of Florida. 
- Drink Up: Taking the Salt Out of Seawater
- Thirsty? How 'bout a cool, refreshing cup of seawater?