WDC water services manager Andrew Venmore said the estimated cost of adding fluoride to all its water treatment plants was $1.5m in capital expenditure in 2014, along with annual operating costs including chemical supply, electricity and staff expenses of about $100,000 per year.
"Should we be required to fluoridate, we would seek funding from all sources possible, including funds allocated by central government."
Far North councillor Ann Court said while the district may be well placed to receive a "larger than others" share of the $12m, it still relied on its communities to fund the shortfall.
"Significantly they will be expected to fund the on-going operations, maintenance and depreciation costs which may be a significant cost for communities already struggling to make ends meet."
And all of that, she said, came without any democratic right to participate in the decision making.
Kaipara District Council, which does not have fluoridated water supply, has not yet considered a fluoridation policy.
Northland District Health Board chief executive Dr Nick Chamberlain said the budgetary allocation to fluoridate water should particularly benefit highly deprived communities, which would result in greater health benefits for them.
"The high rate of dental decay affects general health and well-being and results in significant costs to the health sector - yet, much of this is potentially preventable through public health measures such as community water fluoridation."