Since the time of Julius Cesar (49 B.C.E.), whose Roman legions used solar power to distill saltwater from the Mediterranean Sea, the world's oceans and seas have been looked upon as a potentially unlimited source of drinking water. If only the salt could be removed in a simple, cost-effective way.

During microfiltration, the water passes through straw-like fibers that consist of holes 5,000 times smaller than a pinhole. This effectively pre-treats the saltwater for the reverse osmosis membranes, which consist of holes 5 million times smaller than a pinhole. The water is forced through those membranes at a pressure of 800 pounds per square inch, ensuring most of the salt is removed from the water.

Desalination around the World
Of the more than 7,500 desalination plants in the world, two-thirds of them reside in the Middle East, where there are often no alternative sources of fresh water. Saudi Arabia is the largest producer of desalinated water, operating 27 desalination plants that produce 70 percent of the nation's drinking water, or nearly 800 million gallons of water daily. The plants are also used to generate about 2,800 megawatt hours of electricity each day. Desalination in the Middle East traces back to 1327 when water was so scarce it had to be used as a delicacy. It is also frequently used on islands, such as Malta, off the coast of Italy, which has used desalination since 1881.

The United States' first brush with desalination was in 1791, when Thomas Jefferson discovered a simple distillation process, printed on the backs of papers distributed on ships, giving the sailors the option to produce drinking water in an emergency. The nation's first desalination plant was built much later, in the 1960s, at the oldest overseas naval base in Guantanamo Bay, Cuba. After Fidel Castro's brother, Raul, cut off the base's water supply in retaliation of the Cuban Missile Crisis, Guantanamo Bay became self-sufficient, desalinating 3.4 million gallons of water daily.

Desalination in the United States
Today, less than 1 percent of the population receives water from desalination. In recent years, several desalination plants have been constructed in Florida, but the largest of these, located in Tampa Bay, had to be shut down due financial and technical problems. Although Florida's story is a testament to the challenges we still face in desalination, with the type of research and dedication water agencies across the country are putting into this technology, it should be a feasible option to supplement a dwindling water supply in the near future.

Desalination Process
The process of removing salt from ocean water is called desalination. And the salt removed is measured in parts per million (ppm). Ocean water typically contains 35,000 ppm of salt. Tap water typically contains about 500 ppm, but after the desalination process, it only contains about 350 ppm of salt. While there are a few ways of desalting water, the latest technology employs microfiltration and reverse osmosis.