Wellington Water estimates it'll need one billion dollars a year, to fix its pipe problems.

The water authority says it's in a constrained budget year - as Wellington City Council will this Thursday discuss its financial state.

It comes after Newstalk ZB revealed Wellington Water was aiming to replace 100 kilometres of pipes a year, and had only managed 18.

Chief Executive Tonia Haskell says it's an eye-watering number that shows the level of under investment they've had to date.

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