Revelations Wellington's wastewater treatment plant has been non compliant almost every month for the last two years - after a huge failure yesterday.

Heavy rain flooded the Moa Point plant's lower floors, causing it to shut down and millions of litres of sewage to pour into the ocean.

Wellington Water Chair Nick Leggett told Heather du Plessis-Allan that there's going to have to be significant money spent on Wellington's plants from now on.

He says they haven't had the investment over many years that's needed to keep them up to scratch.

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