Auckland Council is looking to spend a further $600 million to reduce diluted sewage pouring into Waitemata Harbour and onto inner city beaches nearly every time it rains.

The extra money will go to extending a massive new pipeline to reduce overflows and the separation of century-old pipelines carrying wastewater and stormwater.

The council's environment and community committee has given the green light to develop a $1.825 billion water quality programme for the new 10-year budget, $595m more than in the existing 10-year budget.

Funding options are being worked on, but Mayor Phil Goff has signalled a targeted water rate from Aucklanders who benefit from the programme.

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After being confronted with revelations in the Herald in January about one million cubic metres of wastewater and raw sewage pouring into the Waitemata Harbour every year, Goff has set about improving water quality by reducing overflows and, where possible, separating stormwater from wastewater.

The new programme involves an extension to the $1b "central interceptor" pipeline between Western Springs and the Mangere wastewater treatment plant. A new 4.5m diameter tunnel will be built between Western Springs and Grey Lynn.

This would result in overflows at 43 points around the inner city suburbs almost every time it rains being reduced to 10 points overflowing between two and six times a year after heavy rainfall.

New infrastructure would also be built to allow for growth and funding made available to separate stormwater from wastewater where practicable and financially viable.

Dirk Hudig, a spokesman for the Stop Auckland Sewage Overflows Coalition, said the new programme was wonderful news and a sea change for the city's polluted harbour and beaches.

In a presentation at yesterday's meeting, the coalition said water quality in Auckland's western isthmus is unacceptably poor, needs urgent remedial action and urged councillors to prioritise spending on water quality in the new 10-year budget.

"There must be no more deferrals," the coalition said.

Work on the Central Interceptor is due to begin in 2019 - 30 years after it was first mooted in 1989.