Southern politicians are concerned the thousands in savings promised for ratepayers from a massive water reform programme will disappear if Christchurch pulls out.
The reforms revealed by the Government this morning would result in most of the South Island being served by one entity which would control wastewater, stormwater, and drinking water systems.
"Looking at the dashboard for Christchurch, it is difficult yet to see a compelling case for change,'' Christchurch Mayor Lianne Dalziel said.
"I am aware there is more information to come about the full implications for the city of moving the provision of three waters to the proposed new entity.
"Until we get the full package and have all the pieces of the puzzle in front of us, it is difficult to judge whether it is in Christchurch's best interests to be part of the new entity."
Dalziel said the Government is expected to provide councils with more information on the financial implications of transitioning to the new entities at the end of July.
"Once we have that information, we will then need to engage with our communities and get their feedback on whether they want us to continue with the reform process or opt out.''
The Government also released reports showing the reforms would shave thousands off most people's water bills, but a Dunedin City councillor has questioned how these figures were calculated.
Invercargill deputy mayor Nobby Clark said if Christchurch was to opt out of the Three Waters reforms they would not be cost effective for the rest of the South Island any more.
"My understanding is that there is a wavering in the councillor block in Christchurch, it's a pretty even split about whether they'll stay or not."
The Government may remove the ability for councils to opt out to save the scheme, Clark said.
"They may realise... that this is all falling apart on them and the only way to resolve that is to regulate everybody, so you'll have it whether you like it or not."
Clutha Mayor Bryan Cadogan said the decisions of other councils would play into their decision making, with the Christchurch City Council in particular a "huge determinant factor" in the decision.
If Christchurch opted out of the reforms then the rest of the South Island would likely drop below the critical mass required for the reforms to be effective.
He said it was great councils were finally starting to get the critical information they needed to make informed decisions on the issue, but still more was needed.
The decisions the council were facing over Three Waters reform were the biggest he had faced in 20 years in politics.
"We're only about 100 days from having to vote on this, and in between we've got to do our due diligence, we've got to engage with the ratepayers, and we've got to decide which way we are going to go as a council."
The Government's case for the changes said if overhaul goes ahead households in the south would spend an average of $1640 a year on water bills by 2051.
Without the reform, households within the southern entity's boundary would pay an average of $4970 a year, the information suggests.
Dunedin City Council infrastructure committee chairman Jim O'Malley questioned how the Government reached those dollar figures.
"I would argue that it's not clear how good the calculations have been put together by the Department of Internal Affairs... so there's a huge amount of unknown to opting in."
He also said losing control of Three Waters infrastructure would make it difficult for councils to plan for future growth.
"You'd say I want to build a whole new neighbourhood in this area and [the Three Waters entity might say] we won't build the Three Waters for it."
It was unclear if councils which opted-in would be able to reverse that decision at a later date, and he questioned the cost benefits to Dunedin ratepayers of opting in.
- Additional reporting Otago Daily Times