But if the idea of brushing with fluoride makes Connett queasy, the thought of drinking it makes him sick. It is, he says, a dangerous substance that doesn't belong in the human body. "It makes as much sense to swallow fluoride as it does to swallow nail varnish," Connett said.

Unfortunately for Connett and those who think like him, fluoride-free drinking water in the U.S. is becoming almost as hard to find as fluoride-free toothpaste. Fluoridated water flows out of most taps in the country, including those of the great majority of the country's largest cities. Connett, a leader of America's fluoride-is-poison crowd, wants to clear the waters. He and his supporters will have their biggest opportunity in memory on Election Day, when water supplies serving more than 3.8 million Americans will be at stake.

On Tuesday, voters in Salt Lake City; San Antonio; Spokane, Wash.; and several towns from Arizona to Vermont will decide whether to add fluoride to their drinking supplies to improve dental health. Meanwhile, southern Nevada voters will consider whether Las Vegas should flush the compound out of its water system.

Armed with the support of a small group of scientists, the water police hope to build on a base of recent anti-fluoride victories. Once derided as right-wing kooks, they have gained the support of some reputable environmentalists and leftists, including Ralph Nader. But to win at the polls they will have to fight off voter apathy and a reputation as being members of the lunatic fringe. They'll also have to beat back well-funded health groups that have adopted an above-the-fray strategy of refusing to debate their opponents in person.

Fear of fluoride is nothing new, although the opposition movement has gone through various incarnations during the 55 years that scientists and dentists have been trying to dump the compound into public water supplies. Ironically, science first discovered fluoride's benefits in the early part of this century by stumbling upon what happened when people got too much of it. Researchers noticed that children raised in Colorado Springs, Colo., suffered from severe staining and mottling of their teeth, but were also blessed with a low rate of tooth decay. A check of the water supply revealed that it was naturally fluoridated, according to a history compiled by the National Institutes of Health.

Over time, scientists examined fluoride to figure out how much or how little would prevent tooth decay without destroying the teeth. In 1945, Grand Rapids, Mich., became the first major city to fluoridate its water. The cavity rate dipped significantly, inspiring other cities and towns to follow, but it didn't take long for groups like the ultra-right John Birch Society to see fluoridation as an invasion of personal rights.

"The rhetoric of the 1950s is partly crazed and totally paranoid, but revealed a level of distrust and fear that was profound," said Char Miller, a history professor at San Antonio's Trinity University who specializes in the environment. "They saw an attempt of the government to literally invade the body of the citizenry, and in the process dominate their minds and control their behaviors in a way that was emblematic of what we understood the Soviets to do to their own citizens."

Critics didn't have much luck, however, as dentists and health departments clamored for fluoride. City after city began adding fluoride at the rate of about one part per million to their water supplies. Philadelphia, San Francisco and Chicago did so in the 1950s, followed by New York, Detroit and Dallas in the 1960s. Now, according to fluoride supporters, of the country's 50 largest cities only San Diego; San Antonio; San Jose, Calif.; Honolulu; and Portland, Ore.; don't have fluoridated water -- although San Diego's city council recently voted to add the substance to the water supply and Honolulu is considering it.

The most recent federal statistics, from 1992, estimated that 56 percent of the nation's population was served by fluoridated water. The number is certainly higher now since some large cities have joined the trend since then. Fluoridation is not as popular overseas, however. Most countries in Europe, for example, do not fluoridate their water because government officials and scientists do not view it as necessary for the public health.