Water desalination is the process of removing salt and other minerals from water to make the water suitable for drinking or irrigation. The byproduct of this process is brine, which can be processed for table salt. Water desalination is used to produce fresh water in communities where naturally occurring potable water is limited. It is also used to create fresh water for use on ships and submarines.
Due to the specialized equipment involved, desalinating water tends to be more expensive than using naturally occurring water sources, such as lakes, springs, and rivers. For this reason, water desalination is economically feasible only when it would be difficult or impossible to get fresh water from natural sources. One way to reduce the cost of water desalination is to pair the desalination plant with an energy plant and then use the heat byproduct from the power plant to aid in water desalination.
Many countries use desalinated water. Some examples are the United States, Australia, Israel, and Saudi Arabia. Though water desalination tends to be expensive when compared with using naturally occurring ground water, some studies suggest that it is generally less expensive than using large-scale water recycling programs.
There are a couple of methods by which water can be desalinated. One of the most common desalination methods is multi-stage flash distillation (MSF). In MSF, the water is flashed to steam using a series of heat exchangers. Heat exchangers allow heat to be efficiently transferred from one medium to another. As the water condenses, salt and other minerals are left behind.
Another method of water desalination uses reverse osmosis. In this process, a membrane filter is used to remove minerals from the water. Water is pushed at high pressure through a membrane. The water is able to move through the membrane but salt and other minerals cannot. This process is also used to purify fresh water.
Water desalination does raise some environmental concerns. It is difficult to remove water from the sea without harming sea life. Beach wells can solve this problem; however, they limit the amount of water that can be harvested and require more energy.
The other major environmental concern is what to do with the byproduct. Brine byproduct has a salt concentration much higher than natural seawater. This can be harmful to fish if it is dumped into the ocean. This problem can be solved by mixing the brine with the water byproduct from other plants or by dumping it in places where the current is most likely to disperse the salt.