Auckland Council plans $1.7 billion spending on new wastewater infrastructure

It's hoped a $1.7 billion project to clean up Auckland's dodgy drainage will reduce sewage overflow by 80 percent.

Ten beaches across the city are now out of bounds, due to human and animal effluent problems every time it rains over 5mm.

The city's century-old infrastructure means around 1 million cubic litres of contaminated water enters the harbour every year - the equivalent of 400 Olympic swimming pools.

Auckland Mayor Phil Goff says the new infrastructure - including $1 billion ' central interceptor' pipe - will target the city's oldest areas.

"The central interceptor is a new pipeline that's 3.5m in diameter. That will vastly increase the capacity of the wastewater line and stop most of those overflows," he told Newshub.

The rest of the money's been earmarked for upgrading sewers feeding into the central interceptor ($300 million) and a 'waterfront interceptor' pipe, which will feed waste from suburbs on the shore into the main pipe ($325 million).

While it means water bills are likely to rise, Mr Goff says it's a small price to pay to protect the environment.

"It is a lot of money. We will be spending $1.7 billion overall, but I think Aucklanders are prepared to pay for that to make sure their harbours are safe and clean."

It's not clear yet if it's possible or cost-effective to push ahead with all three projects at the same time.

"I think we are all ready to pay a bit more in our water charges to make sure that we have a decent environment, but we all expect Watercare to do this in a cost-effective way," Mr Goff told the New Zealand Herald.

The Mayor also rejected suggestions from his own councillors to scale back on new housing developments. Councillor Mike Lee said the council was "pushing ahead with developments well in excess of our carrying capacity".

"The problem is not the new homes, which have to meet the really strict compliance standards on stormwater," Mr Goff told the paper.

"The problem is the existing 16,000 homes. It would be pretty unfair to blame the new housing, which complies, when the problem is the older housing, which doesn't."

The project could be completed as early as 2018.