ntil very recently, the notion of drinking seawater was lunatic fringe, involving a technology suitable for nuclear submarines and the Middle East, where an oil-rich, water-poor landscape makes financial and practical obstacles irrelevant. In 1960, there were just five desalination plants worldwide. Until the late 1990s, only two American cities had invested in full-fledged desal plants -- Key West, Florida, in the 1980s, and Santa Barbara, California, a decade later. Both cities shelved their plans soon after the facilities were built, having found less expensive sources of water elsewhere. It is still cheaper for Key West to pump freshwater 130 miles from beneath the apron of the Everglades than to desalinate seawater.
However, as desalination technology improves, lowering the cost of producing freshwater, more planners are looking to the ocean as the droughtproof guarantor of continued growth. Throughout the Sun Belt, metastasizing communities have outstripped existing water supplies and begun to look seaward. Last year, municipal water agencies from California, Arizona, New Mexico, Texas, and Florida pooled resources and formed the U.S. Desalination Coalition, a Washington, D.C.-based advocacy group that lobbies the federal government to invest in new desalination projects.
Today there are more than 12,500 desal plants in 120 countries, mostly in the Middle East and Caribbean. Saudi Arabia meets 70 percent of its water needs by distilling salt water; the British Virgin Islands Tortola and Virgin Gorda rely on desalination for 100 percent and 90 percent of their respective water needs. The American Water Works Association, the largest organization of water professionals in the world -- its 4,500 utility members serve 80 percent of America's population -- forecasts that the world market for desalinated water will grow by more than $70 billion in the next 20 years.
California will soon be in the vanguard in the United States. It has already planned or proposed about a dozen desal plants along its coast, including a $270 million plant in northern San Diego County slated for completion in 2007. Early last year, the federal government reduced the amount of Colorado River water allocated to Southern California, forcing the state to accelerate its search for alternative sources after years of helping itself to the dun-colored Colorado at the expense of other western states (and Mexico).
To learn about the potential impact of desalination, I visit Mark Luther at the University of South Florida's Marine Science Center, in St. Petersburg. After a slow drive across the Pinellas Peninsula, traffic congealing at every intersection, I pull into the science center parking lot. It's an early December afternoon, hot and dry, the sky blue from seam to seam. High above the lot, an osprey throws a tantrum, lobbying for issues beyond my comprehension. From the second floor of the building I can see the desal plant across the bay on Apollo Beach, white like the salt it removes. Luther is the oceanographer who studied the bay's circulation patterns as part of the environmental assessment team that helped Tampa Bay Water determine where to site the facility. We settle at a black laboratory table in his bright, cluttered office. Luther, 50, wears a powder-blue yacht club T-shirt and sockless moccasins. His eyes match his shirt. His sand-colored, shoulder-length hair hangs in a ponytail. Luther tells me that, on average, 60 cubic meters of freshwater a second flow into the head of Tampa Bay, courtesy of four main rivers -- the Hillsborough, the Alafia, the Manatee, the Little Manatee -- and a number of smaller tributaries. The freshwater, lighter than salt water, is stirred by the tides before draining into the Gulf of Mexico.
"No matter where you take freshwater, it's going to have some impact on the environment," Luther says. "The goal is to distribute the sources to reduce that impact." Besides operating the desal plant, Tampa Bay Water pumps two new groundwater sites and diverts water from three of the rivers that feed Tampa Bay. "Taking river water has a much larger impact on the bay than the desalination facility," he says. "Of all the ways to get potable freshwater, building a desal plant is no worse and probably better than overpumping well fields or diverting too much river water." It's hardly a ringing endorsement, but it also suggests that an intelligently planned desal plant is not something a sensible environmentalist should lose too much sleep over.
You can't locate a desalination plant just anywhere, however. You need an energy source to operate the plant and a circulation pattern that removes the discharged brine. Brackish water, being less salty than seawater, costs less to desalinate. Hence, the plant was built inside the bay, on Apollo Beach, where salinity, though varying seasonally, averages 20 parts per thousand (ppt), 15 ppt lower than in the Gulf of Mexico. The Big Bend coal-fired power plant sits next door, providing a ready source of water and energy. Of the 1.4 billion gallons the power plant uses each day to cool its condensers, Tampa Bay Water recycles 44 million gallons for desalination. Because the plant already passes intake water through a pair of screens to filter out fish and other sea organisms, from fish eggs to plankton, the desal facility does not cause any additional loss of aquatic life. From the 44 million gallons of salt water it receives daily, the plant produces 25 million gallons of freshwater. The highly concentrated salt water that remains is mixed with the power plant's effluent before being returned to Tampa Bay.
This discharge water adds only marginally to the salinity of the bay, says Luther. A little more than a quarter of a mile from the discharge site he could not detect any increase in salinity. "We're at least an order of magnitude less than natural variability," he reports. The circulating currents and tides, aided by a 43-foot-deep shipping lane dredged decades ago, wash the brine away from Apollo Beach.
Not everyone believes the desal plant is benign. According to an advocacy group called Save Our Bays, Air and Canals (SOBAC), which has its headquarters in Apollo Beach, Tampa Bay takes two years to flush. The briny discharge, SOBAC claims, is equivalent to dumping a truckload of salt in the bay every 16 minutes. The group says that part of the littoral zone off Apollo Beach is already hypersaline. Luther does not believe the desal plant will add to the problem. This part of Tampa Bay flushes about every two weeks during the summer, he tells me, less frequently during the winter. "The waters off Apollo Beach are constantly refreshed. That's why the site was chosen.
"It's ironic that SOBAC brings up hypersalinity," Luther adds. "Probably the biggest environmental disaster to hit Tampa Bay in the last 50 years was the construction of the Apollo Beach community. They dredged pristine mangroves and sea grass beds to build stagnant finger canals and spits of land that are now heavily developed. All those waterfront homes have nice green sodded lawns that require fertilizers and pesticides, which drain right into Tampa Bay."