Councillors have voted to oppose plans to add fluoride to tap water in Southampton.
The debate, at Southampton City Council, was sparked by a 6,000-signature petition against the scheme.
Councillors voted by a majority of about 2-1 in favour of the motion to oppose fluoridation of water supplies, despite having no powers to prevent it.
The plan to add fluoride to the city's water has the backing of South Central Strategic Health Authority (SCSHA).
The authority said it was working with Southern Water on developing an implementation plan.
In a statement, the SCSHA board said it had unanimously decided that "the health benefits outweigh all of the arguments against water fluoridation for the population described in the consultation and remains confident with this decision".
Southampton City Council leader Royston Smith said, even if the government scrapped strategic health authorities in 2013, the council was powerless to reverse the decision to fluoridate water without further legislation.
The council had initially given its backing to the scheme.
The authority had instructed Southern Water to add fluoride to improve dental health in February 2009.
The plan has already been the subject of a lengthy legal battle led by resident Geraldine Milner.
In February, the High Court ruled that the health authority was not acting unlawfully in seeking to fluoridate the water.
Fluoride is currently consumed by 5.5 million people across England.