Christchurch ratepayers might have to fork out tens of millions of dollars to secure the city's water supply and remove added chlorine.
In January, the Christchurch City Council revealed most of the city's 156 wells were at risk of contamination and temporary chlorination for 12 months was essential.
The council initially expected it to cost $630,000 to secure the wells, many of which are below ground, but a review resulted in that cost soaring by more than 500 percent.
In April, staff recommended a better long term solution could be raising 81 wells above ground which, along with other work, would cost $21.5 million.
Staff said UV treatment options could also be explored but this would not be covered in the $21.5m.
They said this would offer better protection, although a staff report stated the increased scope of work "may result in chlorination being needed for longer than 12 months".
The council voted at a meeting today, that raising the well heads and exploring UV options was their preferred approach and the Christchurch mayor, Lianne Dalziel, said she wanted the 12 month timetable kept if possible.
"We've given staff 12 months, if it's going to take more than 12 months they are going to have to come back and tell us why and ask us for permission to continue to chlorinate," she said.
The mayor also said she would consider elevating the issue to a mayoral task force in the future.
Councillor Tim Davidson said the long-term goal needed to remain having a secure water supply free of chlorine.
"Our drinking water supply needs to be gold plated ... it is one the best assets our city has," he said.
Several councillors and the mayor also raised concerns at today's council meeting about the influence of powerful water lobby groups, who were pushing for permanent chlorination across the country.
Lianne Dalziel said there were "big dollars" behind chlorinating water supplies, whilst councillor Aaron Keown said the water industry was "rent seeking".
He said he was worried about "scare mongering" around drinking water contamination issues.
"Water in New Zealand is going to be worth billions of dollars because people are going to pay to protect themselves from something that doesn't exist - no one in Christchurch has ever got sick from our water," Mr Keown said.
Following today's council meeting, staff will now assess every well and bring back a work timetable, which would outline the best option for each well head, to the council in May.