"Water, water everywhere; Nor any drop to drink." That famous line from the old mariner's poem illustrates the conundrum that saltwater presented for humans. There's an almost unimaginable amount of water on our planet, but most of it is held in the depths of Earth's vast oceans -- around 98 percent of it, in fact. The other two percent accounts for aquifers, glaciers, polar icecaps, clouds, lakes, rivers, plants, animals and even our bodies. Add it all up, and the Earth has about 326,000,000,000,000,000,000 (326 million trillion) gallons of water -- most of which is undrinkable and cannot irrigate crops.
Since the days of the mariner's poem, mankind learned how to pull potable water out of the ocean. During his tenure as secretary of state, Thomas Jefferson even required that the process of desalination got printed on the back of every permit for ships leaving U.S. ports [source: Monticello]. The technology was so revolutionary that he wanted to disseminate it among seafarers as widely as possible.
Today, desalination is a common process that's used in seaside cities and towns worldwide. There are more than 15,000 desalination plants around the world providing freshwater from salt and brackish water alike. This number continues to grow as researchers work to improve the process, both in terms of cost effectiveness and energy efficiency.
Salt and other minerals can be extracted from water in two ways: distillation and reverse osmosis. In distillation, salt water is brought to its boiling point. As steam is created, the water vapor separates from the salt, which is left behind in the heating tank. The steam gets captured and cooled in another tank where it condensates as clean, drinkable water. Reverse osmosis acts like a big strainer; water gets forced through a very fine membrane that captures the salt and other minerals. Once its passes through the membrane, the water is ready for drinking.
The upside to these processes is that they are scalable, meaning that you can build a utility-sized desalination plant to serve a city, or a much smaller version can service a village or household. But like everything with an upside, there's a downside. For desalination plants, that downside is energy consumption. The laws of thermodynamics show us that it takes a certain amount of work energy to separate salt from water [source: NIH]. As a result, many municipalities don't take full advantage of desalination because it requires too much electricity.
But countries such as Australia, Israel and even the United States are continually adding desalination plants of various sorts into their water-management portfolios. The facilities are common in North Africa and the Mideast, where freshwater is scarce. In fact, plans for North African nuclear-powered desalination plants were on the drawing boards as recently as 2007 [source: Next Energy News]. And a Canadian company recently won a number of contracts for next-generation of desalination plants that combine solar water heating and an advanced method of reverse osmosis. They claim their process uses 80 percent less energy than current desalination methods [source: LA Times]. Once the problem of energy consumption gets solved, desalination plants might become even bigger contributors to the world's water supply.
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