A former Rotorua mayor has criticised a decision to enter into a $156 million, 10-year wastewater management contract with international consortium Trility.

Former mayor Grahame Hall says Wednesday's decision 'certainly doesn't build back better".

'Many ratepayers are telling me they feel ‘punch drunk' and not listened to with the so-called new way the council is currently operating.”

Hall was the mayor of Rotorua from 1992 to 2004.

He says after Wednesday's decision ratepayers, residents and business people will have 'even more reason to be concerned”.

He says, in his opinion, it's hard to get accurate figures because 'information has been withheld” and the project had been handled in a 'non-transparent way”.

"A seven to four majority is definitely not a good way for [the] council to make such an important decision and speaks volumes of the poor process that has been adopted by [the] council leadership.

'Many in the community hope they will get more information on the deal from the Daily Post's application, under the [LGOIMA].”

On July 28, the council refused to answer 10 questions regarding the proposal's contract and process from the Rotorua Daily Post.

The questions have been re-submitted to the council as a formal Local Government Meetings and Official Information Act (LGOIMA) request.

Hall says he applauds the four councillors who voted against the proposal at Wednesday's council meeting.

'They can call it by another name but it is outsourcing.”

On Wednesday, council infrastructure manager Stavros Michael told the meeting the contract was not 'outsourcing” but 'insourcing” and a 'partnership”.

Yesterday, Michael responded to Hall's comments, saying all costs to buy materials and services relating to Rotorua's wastewater would come from local supply chains.

The exception to that was materials that could not be produced here and had to be imported, he said.

Hall's mayoral successor Kevin Winters has also been critical of the proposal and had submitted in opposition to it at a council hearing on June 25.

In a statement released on Wednesday evening, mayor Steve Chadwick says the council retains 'effective control” over the service and management of the contract locked in the certainty of the cost of it over the next 10 years.

'Action was needed to ensure the resilience of our system into the future.”

Chadwick says the contract 'should be seen” as the council's commitment to protecting the environment, enabling growth in the district and giving certainty that it was taking responsibility and investing in Rotorua's future.

'To not go down this road would have been making the decision to stay with a system that isn't working.”

On Wednesday evening, Michael said in a press release the contract is about 'proactively identifying emerging risk” and about putting a plan in place that 'reduces that risk for an acceptable cost”.

The Rotorua Wastewater Treatment Plant. (File) Photo / Andrew Warner / Rotorua Daily Post.

He says historical underinvestment in the city's wastewater infrastructure meant there was a high risk the system was 'highly likely to experience a critical failure” in the next 10 years.

The impact of such a failure on a critical part of the network could have a 'huge” financial and environmental impact.

The council's 30-year infrastructure strategy - first implemented in 2015 - saw the council commit to funding the renewal of the wastewater network at about 1.5 per cent each year, which was an increase on 0.5 per cent previously allocated, he says.

'While this is an improvement, it doesn't have the immediate impact we need to make real change.

'What we have achieved with this contract is a one-network and holistic approach to the management and delivery of our wastewater services.

'We can guarantee the cost of maintaining and improving our wastewater network will increase in the next 10 years for many reasons.

'Without a holistic approach contract, there is no certainty about what this will cost [the] council. With the contract, we achieve a significant degree of cost certainty.”

Michael says it's 'a different way of doing things” but the development of the proposal had been a 'robust, three-year process” with expert input and two rounds of community consultation.

'I am confident that through this contract we are taking another step towards building the resilient and reliable wastewater services our community demands.”