Voters in Manchester and four suburban communities will decide in September whether to continue adding the tooth-toughener fluoride to their water supply, a vote that will be a rerun in Manchester but a new issue in the towns.

The referendum, to be held during the Sept. 14 primary election, involves the towns of Hooksett, Bedford, Goffstown and Londonderry.

In total, some 90,500 people are registered to vote in Manchester and the four towns. It will be up to them to weigh contradictory claims about the benefits and side effects of fluoridation from a host of different sources.

Gov. Craig Benson signed legislation last month requiring the referendum. The legislation rewrote the state’s fluoridation law after a Supreme Court ruling that invalidated the law.

Already supporters and opponents of fluoridation are organizing and taking steps to get their word out.

State Rep. Barbara Hagan, R-Manchester, is part of Greater Manchester Citizens for Safe Drinking Water Association. She became concerned about fluoride after reading toothpaste warnings that urge parents to contact Poison Control Centers if their child swallows toothpaste.

“I’m thinking, it’s in the drinking water, and coming into our homes. The 2-year-olds are drinking it like crazy,” Hagan said. “I’m not convinced that its benefits outweigh its hazards.”

On the other side, Manchester Mayor Robert Baines supports fluoridation as a public health initiative that provides children with healthy teeth, said his spokesman, Mike Colby. Baines has given the city Health Department the go-ahead to advocate for continued fluoridation, Colby said.

Fred Rusczek, health director for the city of Manchester, said, “Obviously, as the public health director I’m as concerned as the physicians and dentists and others that we’ll go backward on this important public health matter.”

In 1999, city voters approved fluoridation by a 653-vote margin — 51.5 percent to 48.5 percent. Like five years ago, opponents of fluoridation want a debate or forum on fluoridation. Supporters don’t.

Fluoridation foe Gerhard Bedding, a Keene resident and head of the New Hampshire Pure Water Coalition, said much has happened in five years. The Environmental Protection Agency held a forum on fluoridation, at least two Nobel laureates have criticized some aspects of fluoridation, and one recent finding has questioned the effectiveness of ingesting fluoride rather than applying it topically to teeth.

Bedding wonders how long fluoridation supporters can keep refusing to a head-to-head matchup.

“This is beginning to look kind of funny, to claim there is no debate,” Bedding said.

Rusczek said there is no point in debating. Public health issues are weighed by experts on the national level, he said.

“This is not really an issue debated at the local level. If we debated immunization or Vitamin D in milk or folic acid in bread, we wouldn’t have them,” Rusczek said.

He said people should rely on their own physician or dentist for advice. The Centers for Disease Control and Prevention has labeled fluoridation one of the top 10 public health achievements of the last century, he said.

This time around, voters have a clearer sense of what chemical is going into the water. Five years ago, Manchester Water Works would not discuss what fluoride compound they would add to the water until after the election. Water Works decided on fluosilicic acid, a compound that contains minute amounts of lead, arsenic and other toxic metals. Water Works officials have said they purchase the cleanest fluosilicic acid possible. Still, it contains some impurities.

Water works started fluoridating the water in December 2000. Rusczek said it’s too early to see a statistical improvement in dental health in the city. “It’s still a couple of years out,” he said. “It will take a couple of years before we see it.”