Almost half of Wellington's wastewater pipes in 'poor' or 'very poor' condition - modelling

Nick James for RNZ

The decrepit state of the Wellington's wastewater and drinking water pipes has been exposed in the latest modelling from Wellington Water.

The research was completed in May last year and was presented to Wellington City Council at a long term plan briefing in October.

The model took into account factors like pipe age, material, expected lifespan and pipe inspection records.

It showed 44 percent of the capital's wastewater pipes are in a 'poor' or 'very poor' state.

It also detailed that a quarter of the drinking water pipes are in a 'poor' or 'very poor' condition.

Wastewater pipes condition map.
Wastewater pipes condition map. Photo credit: Supplied/RNZ

Wellington Mayor Tory Whanau told RNZ the figures were concerning, but not surprising.

"We've known for some time that our pipes have aged severely over the last few decades and they're at that stage that now they have to be replaced."

Wellington City Council is planning to put a $1.8 billion dollar investment in water infrastructure in its upcoming Long Term Plan.

Whanau said that investment prioritised drinking water pipes, as 18 percent of them were in a 'very poor condition'.

"That's why we have focused in this budget on drinking water and ensuring a lot of our investment goes into the pipes and into the leaks."

She said she was very concerned about the impact wastewater pipes were having on the environment.

"All of us, we all need to do better and that includes Wellington City Council."

Whanau said waterpipe issues were a huge challenge.

"It's a challenge that is becoming bigger than us and that's why me and other mayors are pushing for reform so that we can get a more sustainable model for funding water in the long term."

Water supply condition map.
Water supply condition map. Photo credit: Supplied/RNZ

Wellington Water spokesperson Julie Alexander told RNZ the analysis helped give the council good advice for their funding.

"Understanding where the biggest risks are really helps us to do that."

Alexander said they used a combination of methods to analysis the pipes.

"Often its cameras down into a pipe and then there are also some sonar that we send down a pipe to understand the thinness of the material."

She said the work the had done to assess the condition of the pipes was world leading.

Alexander said they had been mainly focused on understanding where critical pipes were in the network.

In response to questions about modelling, Local Government Minister Simeon Brown told RNZ his immediate focus was ensuring that councils are taking their responsibilities around water seriously.

Brown said the government was also working fast to deliver their Local Water Done Well policy, which he stated will enable councils to move their water assets and delivery services into more long-term financially sustainable configurations.