Audit New Zealand has raised several concerns over Wellington City Council's 10-year budget, which has been adopted this morning.
Audit director Karen Young told councillors many of the council's water assets were old and a significant proportion of them have passed the end of their expected useful life.
"The council has also experienced several high-profile pipe failures, which have affected levels of service."
Young said the council has based the forecast renewal of these assets on their age capped by what is considered affordable, rather than on their actual condition.
"This could result in more asset failures during the 10-year period of the long-term plan, reduced levels of service, and greater costs than forecast," Young warned.