In a just released study, three national environmental organizations call attention to the connection between suburban development and water shortages. Greater Boston loses up to 100 billion gallons of water each year because parking lots, roads and buildings send rain into storm drains instead of into underground lakes, according to the report, titled "Paving Our Way to Water Shortages." And the worst regional drought on record is taking a heavy toll in the Carolinas, where some of the country's fastest-growing cities and suburbs are proving unexpectedly vulnerable to water shortages. "We know sprawl wastes land -- now we know it wastes an astonishing amount of water," said Elizabeth Heyd of the Natural Resources Defense Council, which sponsored the study along with American Rivers and Smart Growth America. But Clayton Traylor of the National Association of Homebuilders said the report's premise was flawed because "water doesn't just disappear." Rainfall that doesn't penetrate the ground is captured in some other closed system, such as a lake, reservoir or stream, he said. Independent water experts cautioned that hydrology makes it difficult to gauge the exact effect of development on natural water flows, but that rapid growth is making more American communities prone to drought. "Because of development, we're much more vulnerable than we've ever been," said Mark Svoboda, a climatologist at the National Drought Mitigation Center in Lincoln, Nebraska.