Wellington Water has requested $6 million to restore fluoride to residents and upgrade facilities.
This is after the water company stopped fluoridation last year at two plants supplying Upper Hutt, Porirua, and Wellington City - without telling anyone.
An independent inquiry into the incident is under way and a final report is due at the end of this month, following which the findings will be made public.
In the meantime, Wellington Water has urgently been assessing how to restore fluoridation at Te Marua and Gear Island treatment plants.
In an upcoming regional council meeting agenda, Wellington Water has requested $6 million (excluding GST) to install a new fluoride facility at each of the two treatment plants.
That money would also be used for upgrades and renewals at existing fluoridation facilities at Wainuiomata and Waterloo treatment plants.
Council officials warned this figure was still a preliminary estimate.
"There remains significant uncertainty and risk which contingencies have been allowed for."
This cost would be funded through the regional council's bulk water levy, which is what it charges city councils for treating the water before it flows through people's pipes.
Greater Wellington Regional Council chairman Daran Ponter said it was a necessary investment.
"We effectively have a social contract here with the public, which says we will fluoridate their water supply and we have committed to doing that in the past."
Ponter said all councillors were all "rather shocked" by the failure to uphold this contract, which was central to the public's trust and confidence in drinking water.
He didn't expect there to be any debate about whether the regional council should allocate the $6 million, as it was effectively a requirement to restart fluoridation.
Meanwhile, the Ministry of Health is also changing fluoridation guidelines, effective from July, and at least 95 per cent of water leaving the treatment plants must be dosed properly.
At the moment there is just one fluoride facility at each plant in the region and Wellington Water has suggested duplicate facilities may be needed.
"To provide back-up options so Wellington Water Ltd can continue to fluoridate drinking water if a facility fails or needs to be turned off for maintenance work", the council agenda said.
Wellington Water is working on a strategic business case for a second tranche of funding for this, which will be presented to the council in the current financial year.