Fresh Water From the Sea

The people of Coalinga, California, used to have their fresh water shipped in at a cost of about $7 a thousand gallons. Now the town's drinking water costs less than a fourth as much, thanks to a new 28,000-gallon-a-day desalination plant that lowers the salt content of brackish wells from an undrinkable 2,000 parts per million to a quite tolerable 300. A much larger plant—275,000 gallons a day—now being built on arid St. Thomas in the Virgin islands is expected to convert sea water for less than $5 a thousand gallons now paid for bringing fresh water in by barge. In Freeport, Texas, the new 1,000,000-gallon-a-day plant, built and operated by the Department of the Interior as part of a demonstration program, is reducing the salinity of Gulf of Mexico water from 35,000 to 50 or less parts per million within a cost range of $1.00 to $1.25 a thousand gallons.

A number of other such practical results are beginning to flow from recent research and development work in desalination. Yet there is still a long way to go. Not many towns or cities in the United States pay as much as 30 cents a thousand gallons for municipal water supplies. The big question mark is cost. Anyone with a teakettle, a flame, and something to trap and condense the steam can turn saltwater into fresh. Men have been doing this for centuries. The hitch is that such primitive methods yield so little or, if tried on a larger scale, cost so much.

During the past decade, as more and more American cities began to worry about future supplies of freshwater and as scarcity of water was noted as one of the big problems in many of the countries to which we are giving economic aid, great advances have been made toward better methods. Many of the new processes are simply large-scale and ingenious improvements in distillation—the old teakettle method—by use of unconventional fuels (including sun power, the oldest fuel of all), or by new adaptations of the principles of vacuum or compression. Another promising line of attack is ion exchange, by which mineral particles migrate through a membrane until the water on one side is nearly fresh, while on the other it becomes more salty. A third approach is through freezing; the ice that forms first is composed of nearly pure water. Still other methods are being tried. Progress is continuing, but as yet the cost barrier has not been broken, or even much more than chipped.

Irving Fox, vice president of Resources for the Future, sums up the situation in an article for The Bulletin of the Atomic Scientists. The gist of what he says is this: Desalination has been much discussed as the most promising way to increase freshwater supplies. Though not directly usable by men or crops, saline water is unlimited. Arid lands in many places are near the oceans. Prospects of low-cost fresh water from the sea recall the biblical vision of making the desert bloom.

The trouble is that costs for the several processes that are being studied remain relatively high, the lowest yet attained being about $1.00 a thousand gallons for freshening sea water. Current reports suggest that these costs may be lowered to 40 or 50 cents a thousand gallons. For brackish water containing about a tenth as much salt as sea water, current costs are about 30 cents a thousand gallons. In contrast, the upper limit on the value of irrigation water in the United States is about five or six cents a thousand gallons. Few irrigation farmers can afford to pay much more than half that price. It is doubtful that farmers in low-income countries could afford to pay much more than one cent per thousand gallons for irrigation water. Municipalities in the United States could probably afford to pay 25 cents or 30 cents a thousand gallons, and a number actually do; but towns and cities in most areas can get their supplies for considerably less. Accordingly, the outlook now is that desalinization on a commercial basis will be limited to a relatively small number of locations where cities and industries can afford rather high-cost supplies. Only a first-class technological breakthrough can alter this outlook.

One answer is continued research and development, not only in desalinization but also along other technological lines, both those that might actually increase supplies of fresh water—such as cloud seeding and other forms of weather modification, and those that might stretch supplies by reducing losses from evaporation—like replacing water-thirsty trees in dry areas with shallow-rooted grasses, or protecting reservoir supplies with a single-molecule plastic film. But none of these methods is as yet dependable. Consequently the job of getting the most out of water resources still must be done largely by familiar methods: more dams to store water for use during periods of low stream flow, better means of reducing industrial and household pollution, and more attention to making sure that water supplies in each area are used for purposes that will bring the highest returns.