In Search of a Drought-Proof Source - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 286

he oceans hold 321 million cubic miles of water . When salt is dissolved in water,
it breaks the ionic bonds that bind salt crystals together; removing those resulting salt
ions requires a lot of energy. The problem with distilling seawater is that it requires so
much energy that it can be used only in small shipboard systems, or in places such as
the Middle East where money and fuel are plentiful and freshwater is scarce.
A few “multi-efect” distillation plants , which use a cascading system of chambers,
were built in the early nineteenth century, but mineral deposits on heat exchangers
hampered the system. By the mid-twentieth century, a second method was developed
that pushed salt water through a set of fine semipermeable membranes, which remove
most of the salts. The best-known form of this process is called reverse osmosis, or RO.
In 1965, an experimental RO plant was built in Coalinga, California. And in 1980,
the world's first municipal seawater desal plant opened in Jidda, Saudi Arabia. These
early plants required huge amounts of energy to run (the Jidda plant needed more than
eight kilowatt hours [kwh] of electricity to produce one cubic meter of drinking water)
and were considered too expensive and technically complex to be widely popular. Fur-
thermore, the membranes were expensive to make and difficult to keep clean.
But the dream lived on. Cruise ships and aircraft carriers, arid seaside resorts in the
Caribbean, and wealthy petro nations in the Middle East began to desalinate water reg-
ularly. This pushed down prices and led to the development of new technologies. Today,
greater economies of scale, improved energy-recovery devices, and more sophisticated
membranes have lowered the cost further, making desal on a larger scale more feasible.
During the extended drought of the late 1980s, several desal plants were built along
the California coast. One was operating in Santa Barbara , but three months ater the
plant was completed, the drought abruptly ended with a series of drenching rainstorms
referred to as the “March miracle.” The Santa Barbara plant was mothballed. (Much of
the equipment has been sold off or is obsolete, and the city's homeless have taken up
residence around the plant's perimeter.) Since then, refinements have brought down the
cost of desalting ocean water from about $2,000 an acre-foot in 1990 to about $800 in
2007, which was slightly above the cost to coastal California cities of importing water
from the Sacramento Delta and the Colorado River.
By 2005, more than two thousand desalination plants were operating in the United
States, and today many more are on the drawing boards. The American Water Works
Association, a trade group, predicts the desalination business will grow by $70 billion
over the next two decades.
Not all desal plants are built on the ocean. About a quarter of them, such as the
planned American Waters plant on the Hudson River , just north of New York City, pro-
cess river water. Others, such as the Bureau of Reclamation's Yuma Desalting Plant in
Yuma, Arizona, process brackish inland water. Because inland water has less salt and