Campaigners handed a petition with 14,000 names to Downing Street
Southampton City councillors have voted to call on the South Central Strategic Health Authority to hold a referendum on its move to add fluoride in water.
Health bosses agreed the plans for the city's water in February last year despite 72% of 10,000 respondents in a public consultation opposing the move.
The move is the subject of a judicial review after a resident launched a private legal challenge last June.
But the health authority said it "has no mechanism to hold a referendum".
It said mass fluoridation was a "safe way" of tackling tooth decay.
A spokesman said it was confident the decision was "in the best interests of the health of local people".
As a result of the authority's move, activists from Hampshire Against Fluoridation and other supporters delivered a petition with 14,000 signatures to Downing Street on 9 June last year.
Resident Geraldine Milner is behind the legal challenge against the decision by the SCSHA.
The judicial review will be based on government policy, which states most residents need to be in favour of the move.