A Sea Change In The Search For Water

New technology could make desalination more affordable

Rainfall and healthy aquifers once provided more than enough drinking water for the residents of the Tampa Bay region. But recent droughts and a threefold increase in population, to 2.3 million, since 1970 have forced the city to find a new source. That turns out to be something closer at hand than most residents expected: the briny sea. Tampa Bay, which rises from Florida's west coast is now a test site for new ways to extract freshwater from the ocean.

Tampa Bay's water problems aren't unique. Of course, freshwater is scarce in many Western states. But even in the Eastern U.S., droughts and diminishing groundwater supplies have left communities in Georgia, Virginia, and Maryland feeling parched. As a consequence, many people are watching the Tampa Bay experiment with intense interest. Desalination could emerge as one solution to water shortages in numerous coastal communities if the techniques under development there prove cost effective and if environmental concerns--such as where to put all the salt that is removed--can be addressed.

Making saltwater fresh is nothing new. For thousands of years, seafarers have known that seawater can be evaporated and the vapor collected and cooled into pure freshwater. Today, many countries in the Middle East use their abundant oil supplies to boil away impurities in seawater. And many have experimented with large-scale electrolysis.

That approach has never been economical in the U.S. But since the 1950s, researchers have experimented with membranes punctured with microscopic holes that filter out large salt and mineral molecules while allowing smaller water molecules to pass through. The scientists have been especially keen on a technique called reverse-osmosis filtration, where seawater is forced through a series of selectively permeable membrane filters. The technique works quite well in the lab, but the membranes have been prohibitively expensive for large-scale use.

Until now. Thanks to enhanced competition among membrane producers and improved production methods over the past several years, membrane material costs 20% of its 1980 price. Membrane technology "is now a viable alternative," says Patricia A. Burke, secretary general of the International Desalination Assn., based in Topsfield, Mass.

By the time the Tampa Bay Seawater Plant goes online on Dec. 31, 2002, it will be the nation's largest seawater processing unit. It will pump out 25 million gallons of freshwater per day--about 10% of the daily volume for the region--at a cost of just over $2 per thousand gallons.

That's not exactly cheap: Tampa Bay residents currently pay around $1.40 per thousand gallons. But with freshwater supplies shrinking and demand growing, investors are betting that communities will have little choice. "We understand the economic drivers for this project. People need water. We're delivering water as a product," says Scott H. Pearce, senior vice-president for project development at Poseidon Resources in Stamford, Conn., the leading investor in the $100 million Tampa Bay seawater plant. The region's water utility, Tampa Bay Water, also recognizes the mandate. It inked a 30-year deal with Poseidon and its partners to buy water for the city from the new plant. The deal is one of 10 projects Tampa Bay Water is pursuing in an effort to secure the city's water supply.

And the taste? There is none, says St. Petersburg Mayor David J. Fischer, who also chairs Tampa Bay Water. "The clarity was excellent," he adds, noting that the desalinated water will be blended with freshwater sources.

LAGOON BLUES. But some environmentalists are uncomfortable with this arrangement. For every 4.4 gallons of water the Tampa Bay plant produces, it sends 1.9 gallons of concentrated saltwater back into a nearby lagoon. "We're not against desalination. We know the future of our water supply is going to depend on it," explains Bob J. Bettis, vice-president of Save Our Bays & Canals. "We're against the discharge in the shallow estuary instead of farther out in the Gulf." Bettis is worried that the shallow waters around Tampa Bay won't be able to dilute the salt quickly enough to avoid harming marine life.

Other thirsty communities are considering Tampa Bay's experiment. Indeed, Poseidon has partnered with the regional water agency of Orange County, Calif., and is pursuing agreements in San Diego and Freeport, Tex. If its new technology yields quality drinking water at prices people can stomach, many cities may discover that the hunt for freshwater comes down to the sea.

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