Tina Worley, age 14, of Santee, Calif., for her question:
CAN'T OCEAN WATER BE USED TO SOLVE DROUGHT PROBLEMS?
About 97 percent of the water on earth is salty ocean water. That means only 3 percent of all available water can be used for man's drinking purposes, irrigating his fields and supplying his farm stock. The ever increasing demand for fresh water makes almost everybody turn to the ocean where the hope for future extra water must be found.
Removing salt from ocean water so that the fresh product can be used to solve the world's drought problems is something that man has been considering for many years. The process is called desalinization.
One of the major drawbacks to the desalting program planned to turn ocean water into fresh water is that the procedure is slow and that it is also very expensive.
It takes a great deal of energy for desalinating water, and energy is expensive whether it comes from nuclear power plants or from hydroelectric sources. Experts figure it costs about one dollar to produce 1,000 gallons of fresh water from ocean water while it costs only 30 cents to distribute the same amount from fresh sources.
But expense is a problem that may someday be solved.
More than 200 desalting plants have been built throughout the world. They're located from California to Australia and from South America to Greenland. Most are small and are used for oil drilling crews in the deserts or for people on island resorts. They're all near the oceans since transporting water inland can add greatly to costs.
The oldest method and most common for removing salt from seawater is with distillation. Many ships used this method for obtaining drinking water. Water is boiled, salt is left behind and the steam cooled in coils comes out as fresh water. Navy stations at Key West and Guantanamo each produce over 2 million gallons of water a day using the distillation method.
Another method is electrodialysis. Electric current is sent through special chambers and water in them is charged so that salt is left behind. A plant in Webster, S.D., now produces 250,000 gallons daily from brackish ground water.
A government plant in Wrightsville Beach, N.C., uses a freezing method and now produces about 200,000 gallons daily.
A most promising method is called reverse osmosis in which water will flow through a semipermeable membrane. With pressure, fresh water will be squeezed from the salt water as it passes through the membrane.
Government and private research is also looking toward nuclear powered plants that will both desalt water andalso produce electricity. Good things will be coming up soon.