Half of Wellington's rivers and streams are now graded as having unacceptable levels of e-coli, as the fallout of a "huge investment hole" continues to come to light.

An urgent meeting has been called over the state of the city's water infrastructure after two major wastewater pipelines failed within a month of one another and burst mains left hundreds without water in their homes.

But streams and rivers have been feeling the effects of underinvestment in water pipes for many years.

Greater Wellington Regional Council monitors 45 sites across the region.

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The latest figures show 47 per cent are graded E or D for e-coli, the lowest possible ratings.

Large urban streams like Kaiwharawhara, Porirua and Karori were all graded E, which is considered representative of all urban streams in Wellington.

Regional council urban water management programme leader Alastair Smaill said the degradation of urban streams was "death by a thousand cuts".

"This has sort of crept up on us over a long period of time. We've had more development, population increases, and effectively that infrastructure is now starting to sag under the burden of that increase.

"Now it's got to a point where we're not only seeing that base level of leakage from the system but we're also seeing some catastrophic failures like we saw in Willis St just before Christmas, so those big failures are starting to happen a bit more often as well," he said.

The state of the infrastructure itself was also to blame, he said.

"It's a huge investment hole, we're talking here about a multi-billion-dollar problem we have and obviously you can't fix that everywhere immediately. That's sort of the inconvenient truth, that it's actually quite a big problem."

Wellington-based National list MP Nicola Willis says the city has to confront the state of its infrastructure. Photo / Mark Mitchell
Wellington-based National list MP Nicola Willis says the city has to confront the state of its infrastructure. Photo / Mark Mitchell

The Karori Residents' Association has been lobbying Wellington Water to install a sign warning the public about the poor water quality at Karori Stream.

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But a Wellington Water spokesman said streams were not recognised bathing areas so water quality and related information was not posted at sites like Karori.

"We continue to support the Karori Residents' Association in their intention to place information signage at a point of their choosing, on their initiative, in a way that meets that community's needs, and are ready to help with the information content they might want to include", he said.

Wellington-based National list MP Nicola Willis said people using the stream deserved to know there was a risk.

"It's one thing to have a sign from a residents' association, well-meaning as it may be, it's another thing to have the stamp of authority on it.

"Karori residents want Wellington Water to front up, to be accountable, and put up the signs", she said.

Fixing the infrastructure to turn around the fate of the streams is expensive and complicated.

In some cases pipes will need replacing, but other contamination stems from what is known as cross connections, where wastewater from private homes is plugged into the stormwater.

In other situations, there are no connections at all.

Smaill said progress on improving water management was being made through the Whaitua Implementation Programme and real change could only be driven by the community.

"When they are really aware of what's going on and have that connection with their own water bodies, it's only then that they will shout very loudly and will probably be more likely to put their hands in their pockets and pay some rate money for that.

"Until you get to that point, it's all just too hard", he said.