Question:
Twelve years ago, when a new gasoline additive held the promise of reducing air pollutionin detail?

Answer: six years later, when studies began to show that the chemical was a potential carcinogen, state officials realized that by trying to clean the air, they may have seriously damaged the water supply. M.T.B.E. had been leaching into the underground water table from thousands of gas tanks, and now the state has more than 13,000 spills that must be cleaned up, one of the worst cases of drinking-water pollution in the nation, experts say.

As a result, far fewer people have been staying at Annie Scott's bed and breakfast, a two-story Victorian house with a scenic view of the Bear Mountain Bridge on the Hudson here in Orange County. Even though Sunoco installed a purifier in her basement and the company conducts regular testing on her well, Mrs. Scott says the water still smells like turpentine. She refuses to serve it to her guests, drink it herself or give it to her two teenage children.

"We offer bottled water if guests want to brush their teeth, make coffee, or take a drink," said Mrs. Scott, who estimated that she had lost $15,000 worth of business each year since an underground leak in December 1999 at a nearby gas station contaminated local water with M.T.B.E. "We also warn guests about showering, since M.T.B.E. is worse when it vaporizes."