Facing a severe shortage of fresh water, the sprawling Tampa Bay area is planning to build the largest desalination plant this side of Saudi Arabia by the end of 2002. If the plan is approved by state environmental officials, Tampa Bay envisions desalted sea water providing about 10 percent of the drinking water for the region, whose population has grown fivefold in the last 50 years to 2.3 million. Some locals welcome the plan because it calls for cutting down on groundwater pumping, which damages wetland ecosystems. But others argue that it could hurt sea life because Tampa Bay would have to absorb the main byproduct of desalination, a briny concentrate. The price of desalination is coming down and more U.S. cities are likely to consider it in the future.