Desalinizing sea water

With the oceans holding 97% of all the water on earth, desalination of sea water might eventually offer the solution to a limited renewable supply of fresh water. Several desalination technologies, such as distillation, electrodialysis and reverse osmosis, have been developed, but since they are highly energy-intensive, they are so far too expensive for use except by countries that have non-marketable supplies of natural gas or islands that depend on tourism for a large share of their income.

Fresh water sustains human life in a variety of ways. We need to drink it every day to replenish what we lose through perspiration and excretion. With few exceptions, all of the foods we consume, whether plant or animal, need abundant fresh water to grow. Not least, the virtually all of the living environment needs a supply of fresh water.

The Arab oil rich countries such as Kuwait, Qatar, Bahrain, Saudi Arabia and the United Arab Emirates are five out of nine countries in the world which have the least per capita water resources. Kuwait and most of other Arab emirates rely on desalinating sea waters in order to meet their needs for sweet waters. At present, 60 percent of water desalination capacity of the world is concentrated in the Persian Gulf. The water desalination capacity in Saudi Arabia alone accounts for 30 percent of the overall capacity of the world.

Israel desalinates water at a plant in the resort town of Eilat. But experts say desalinization in large enough quantities to matter to settlement areas is currently too expensive to consider.

Researchers at the University of Delaware have developed a simple and inexpensive device that uses wave energy to desalinate sea water. The device is called a Delbuoy ("Del" refers to the University of Delaware, and "buoy" refers to a buoy that rests on the water's surface). When the waves lift and then lower the buoy, a piston connected to the bottom of the buoy drives a pump at the sea's floor. The pressure created by the piston is strong enough to drive the sea water through a reverse osmosis filter, which removes salt and impurities from the water, and then to send the fresh water through a pipe to the shoreline, where it is tapped and used by people. Local divers with simple tools can install the devices in just ten minutes. The units cost little initially and can be maintained by trained local individuals. Best efficiencies are attained when the pump is deployed at depths of at least ten meters, and in the trade winds region from 30 degrees South to 30 degrees North latitude.

To get fresh water from the sea in sufficient quantities you need to be able to provide and pay for the fossil fuels or other energy sources, such as nuclear power, that the desalination plant requires. These costs are quite high, particularly when added to the costs of building, staffing and maintaining the plant. Since burning fossil fuels and producing nuclear energy present, beyond their financial burdens, risks to human health and the environment, building a conventional desalination plant becomes an even more difficult decision.