A group trying to remove fluoride from Canada’s water supply said an Ontario municipality’s decision on Tuesday to stop using the chemical additive was “ground zero” for its national movement.

But the incoming head of the Ontario Dental Association warned the decision sets a dangerous precedent by allowing a small minority of people, using questionable science downloaded off the Internet, to effect dramatic change on public-health policy.

“My greatest fear here is with the advent of the Internet, and with the advent of social media, that a small vocal minority of individuals who are perhaps misinformed are able to reach a great number of people,” said Dr. Harry Hoediono, the association’s incoming president and a dentist in Waterloo, Ont.

The municipality of 500,000 an hour west of Toronto voted on Tuesday to stop using fluoride, which has been in the local water supply since the 1960s.

Public-health officials and dentists have urged municipalities to keep fluoride in the water, saying it prevents tooth decay, saves millions in public-health costs and protects children, the elderly and the impoverished, who might not have access to regular dental care.

Opponents of fluoride, citing dozens of studies, have called the chemical an illegal and unnecessary drug that is responsible for cancer, thyroid disease and a rash of improper arthristis diagnoses.

“People are starting to realize that there’s no science supporting drinking fluoridated water and there’s no science supporting that it’s safe,” said Robert Fleming, of the group Canadians Opposed to Fluoridation that launched the anti-fluoride campaign in Waterloo and is trying to court other municipalities across the country. “And people are getting angry.”

The group launched a two-year battle to oust fluoride after two residents complained they had serious health complications from fluoride sensitivity, culminating in a public referendum last month that narrowly supported getting rid of the additive.

Although “virtually” every Waterloo councillor supports fluoridation, they voted unanimously to remove it because they wanted to respect the results of the referendum, said regional chairman Ken Seiling.

He blamed fluoride supporters, including the area’s dentists, for not mounting a more effective public awareness campaign.

“I think this is really most unfortunate and, quite frankly, I don’t accept a lot of the information put forward by the anti-fluoridation group,” Mr. Seiling said. “But I have to live with the results.”

The battle over fluoride, which was first introduced into the water supply in Canada in the 1940s, has given rise to a growing movement across North America. In the early 2000s several communities in British Columbia voted to get rid of fluoride, as did Whitehorse in 1998, while in 2007 a group of 200 dentists unsuccessfully lobbied U.S. Congress to remove the chemical additive from the water supply.

There has been a recent series of municipal votes or public referendums on fluoride across Ontario — where policies on fluoridation are left up to municipalities — including in Halton, Niagara and Thunder Bay. However, Waterloo appears to be the first in the province to actually remove fluoride.

But while Ontario’s chief medical officer of health called fluoridation “one of the greatest public health achievements of the 20th century,” the provincial government has no plans to change the legislation to wrest control over the issue from municipalities and force province-wide fluoridation.

“No, we are not considering making fluoride mandatory across the province,” said Ivan Langrish, a spokesman for the Ontario Ministry of Health and Long-Term Care.

Health Canada convened a panel of experts in 2007 that found that fluoride was safe in the drinking water at current recommended levels and was an effective tool in the fight against tooth decay.