The authority in charge of adding fluoride to Southampton’s water has yet to set a timetable for the scheme, even though it will be disbanded in 2013.
The South of England strategic health authority (SHA), which is due to be scrapped in March, insists fluoridation of the city’s tap water will go ahead.
The admission comes as campaigners urge the government to halt the process.
The Hampshire Against Fluoridation (HAF) group is concerned that fluoride could have adverse health effects.
In a letter to the Secretary of State for Health Andrew Lansley, HAF chairman John Spottiswoode urged the government to channel money for fluoridation into child dental services.
The Department of Health said decisions on the fluoridation of drinking water – which aims to reduce tooth decay – should be taken locally.
The SHA agreed to a request by NHS Southampton City in 2009 to add fluoride to tap water in Southampton and parts of south Hampshire but, when asked for an update, a spokesman said no timetable had been set.
Southern Water, which would carry out the fluoridation, said: “An updated feasibility study is ongoing and we are in regular correspondence with the Strategic Health Authority as part of this.”
Mr Spottiswoode said: “With less than eight months before the SHA is abolished, the details of the scheme have not been finalised, Southern Water cannot say which areas would be fluoridated and we have no idea of costs and there are no published details of the scheme – obviously a ridiculous situation.”
Following the government’s abolition of the SHAs, which forms part of the Health and Social Care Act, decisions over fluoridation will rest with councils.
Southampton City Council said it was not aware of any imminent plans by the SHA to implement the scheme.
A Department of Health spokesman said: “Currently strategic health authorities conduct consultations on proposals for fluoridation but, with effect from next April, this responsibility will transfer to local authorities.
“We will be shortly conducting a consultation on the detail of these changes which we propose to make through regulations and will be inviting comments on the process.”
The fluoridation of Southampton’s water has already been the subject of a 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.