Southampton City Council was expected, with neighbouring authorities, to exploit new powers to block the move – aimed at cutting tooth decay – which is due to start next year.
But the cash-strapped council has now suggested it lacks the money to stage the detailed public consultation required to overturn the decision.
Instead, the Labour-run authority appears happy to cross its fingers and hope the new body in charge of fluoridation lacks the will to force through the measure.
Richard Williams, the council leader, told his local newspaper he could not justify the expense of a consultation – but insisted fluoridation would not be a priority for Public Health England (PHE).
He said: ‘Just because an agreement is there, they won’t want to do it because it’s not a popular scheme. So, therefore, is it something a new body is going to want to do and put people’s backs up?’
However, Councillor Williams promised the Southampton public that he would consider how to act if PHE did try to implement the scheme.
PHE is a new health quango that started work on 1 April, although responsibility for public health in each area now rests with local authorities.
For that reason, Southampton has the power to overturn the fluoridation decision made – four years ago – by the now-axed South Central Strategic Health Authority (SHA).
However, the Department of Health (DH) unveiled what it called clear guidelines on how consultations should be carried out – to make further judicial reviews less likely.
Setting up the Southampton scheme had proved to be a 'time-consuming and costly process', running up a legal bill of £350,000, ministers pointed out.
A High Court legal challenge has already put fluoridation on hold for 18 months and agreement with Southern Water has also taken much longer than originally expected.
The SHA had said it expected fluoridation to be up and running in parts of Southampton, Eastleigh, Totton, Netley and Rownhams in 2014.
Permission is classed as ‘existing’ and work on it will continue despite the SHA’s demise – subject, it appears, to PHE’s will to act.
In 2012, Southampton council voted against plans to add fluoride to tap water, following a 6,000-strong petition against the scheme.
By Rob Merrick, parliamentary correspondent