Critics say fluoride has been linked to health problems
Councillors in Southampton have voted to add fluoride to tap water in the city and west Hampshire.
Southampton City Primary Care Trust wants the level of fluoride increased to one part per million which it says would cut tooth decay.
Health chairwoman Edwina Cooke said 26 councillors voted for it and 18 against after a heated debate on Wednesday.
Campaigners against fluoridation said the council had "ignored the wishes of their electors".
Ms Cooke, who voted against the move, added: "They changed their mind three times - 94% of councillors spoke."
The council will now make official representation to Southampton City Primary Care Trust.
I don't think fluoride for everybody is the answer to keeping children's teeth healthy
An independent board for the South Central Strategic Health Authority (SHA) will then assess the votes from the various authorities.
The 14-week public consultation, which ends in December, is being independently-run by the SHA, which will make the final decision in February.
Earlier, Hampshire PCT put its weight behind the idea but said views of all residents across the county should be taken into account.
Opponents claim fluoride has negative effects on the body.
John Spottiswoode, chairman of Hampshire Against Fluoridation, said: "It makes one ashamed to live under a council that is quite happy to force people across the city to drink water that is contaminated with a known toxin.
"When most countries across Europe have tried water fluoridation and abandoned it as ineffective and dangerous, why should we in Southampton be forced to go down this scientifically discredited route?"
If the plans are approved more than 200,000 people would be affected.
Ms Cook, who heads the Healthy City scrutiny panel, added: "I don't think fluoride for everybody is the answer to keeping children's teeth healthy."
Southampton City Primary Care Trust said it was pleased with the decision.
Andrew Mortimore, public health director at Southampton City PCT, said: "We hope that local people take confidence from the decision taken by the city council to back the proposals."