WDC in June became the first council in New Zealand to opt out of the Government's multi-billion dollar three waters reform plans.
Council resolve on opting out has intensified with the new report, its investigation into the Northland-based entity the result.
WDC is one of New Zealand's strongest-placed councils in terms of its three waters infrastructure investment and its financial position around that.
However, the government department playing a key role in the three waters reforms has hit back at WDC and its report.
"We know Whāngarei (District Council) believes it is in relatively good shape compared to a lot of councils - at the moment. But we are talking about setting up a system that will safeguard our services for generations to come," a Department of Internal Affairs (DIA) spokesperson said.
Mai said other councils around New Zealand should make sure they were robustly investigating local implications too. They would also soon have access to the WDC-commissioned report.
WDC's stance comes in spite of the council standing to gain $133 million from the Government which includes significant deal sweeteners for them to join its three waters reform.
Mai said there was more to the reforms than the money.
She said the council's new report clearly showed the costs and benefits for Whangārei put
forward by the Government in its national three waters sector restructuring plans, were not the case locally.
Government figures said under its three waters plans, Whangārei residents would pay $803 annually for their three waters services by 2051 - if WDC joined into amalgamation processes. It said if WDC did not join in, that figure would rise to $4055 a year.
Mai said that was not the case.
The new WDC-commissioned report has been done by Castalia, an international company with offices in Auckland and Wellington that advises globally on infrastructure, resource management and policy in areas including water.
"The reform scenario is based on faulty assumptions and flawed analysis. The government has not shown with sufficient certainty to WDC that the claimed benefits of the reform scenario will materialise," the Castalia report said.
Mai said other councils around New Zealand were considering the matter too. Robust investigations should be carried out on their parts.
"This report has shown that the reform scenario is founded on unsound evidence and faulty analysis. The promised benefits of reform are unlikely to materialise. There are risks to the Whangārei community from losing control of water services, and accountability of those tasked with governance to local customers," the report said.
Mai said WDC's report served only to strengthen council's resolve around its provisional opt-out decision.
The DIA spokesperson has however, in response to the release of the report and the Mayor's comments said they were still to understand the basis of the claim in Castalia's report.
"While we are still working to understand the basis of the claims made by this consultancy we can say that their earlier work on the reform proposals commissioned by Local Government New Zealand was found wanting by the joint central/local steering committee which includes (Local Government New Zealand) LGNZ representatives and mayors as well as officials," the spokesperson said.
The Water Industry Commission for Scotland (WICS), which the Government used to put together its future water infrastructure and servicing cost estimates, had done this work using information provided from New Zealand councils' own data.
Future water infrastructure and servicing cost estimates could be even greater than those presented in the WICS analysis as it had not taken into account climate change or seismic risks, peer reviewing of this analysis had shown.
Mai said WDC would continue to operate in the best interests of its people through any restructuring. That was why it had opted out of the Government's proposal in June.
Considering its people would also be part of considerations in any Northland-based three waters entity.
She said FNDC and KDC would be doing the same for their people, with financial implications for all councils, even with the locally-generated proposal.
Mai said three waters costs would still increase under a Northland-based entity in line with higher expectations nationally around things like water quality.
She said improving water quality was worthwhile.
It was a matter of looking at how the district and the region best approached three waters into the future for the benefit of its people.
