The independent inquiry into Whanganui's failed wastewater treatment plant has cost ratepayers just over $54,000.

The figure was released on Wednesday by Whanganui District Council chief executive officer Kym Fell.

Mr Fell said the final cost was $54,180 which included professional fees paid to Robert Domm, who handled the inquiry and prepared the 200-page report, as well as his accommodation costs and one return economy airfare to Australia.

Mr Domm left Sydney for Whanganui on July 13 and returned to Sydney on September 10, a period of just over two months.

Advertisement

When council decided to carry out the inquiry, it set aside 90 days and a budget of up to $100,000 for Mr Domm to investigate and write up his report.

"Ultimately this review was achieved in less time resulting in a lower cost," Mr Fell said.

Mayor Annette Main said given the inquiry was completed well within its timeframe and at a cost less than budgeted was pleasing. And she said the circumstances surrounding the failure of the plant, in particular the involvement of three different councils, justified the inquiry being commissioned.

She said if the recommendations from Mr Domm's report were adopted as council policy - "changes this council has already made to its practices" - they will bind future councils.