Historically, Auckland City has used the same pipe to transport stormwater and wastewater. However as Auckland has developed, some of the natural drainage points (such as grass areas) have reduced – forcing more water through our stormwater system.

In times of heavy rain, this combined pipe is unable to cope and can cause diluted sewerage to overflow into open waterways, streams and harbour waters.

An important environmental focus for Metrowater is on separating the combined network so there are separate pipes to transport wastewater and stormwater - reducing the likelihood of polluted overflows entering the harbour.

The Clear Harbour Alliance, a joint partnership between Metrowater, Works Infrastructure, GHD Limited and Opus International Consultants, is currently focusing on separating properties in Kingsland and Mt Eden from the combined network. This project is expected to substantially reduce the annual volume of sewage pollution entering the Waitemata harbour around Westmere and Saint Mary’s Bay.

This project further builds on the work Metrowater has already undertaken, investing more than $65 million over the past decade in capital works to cut overflows – including $16.9 million on completing sewer separation works in the Pt Chevalier, Orakei Basin and Upland areas.

About 15% of Auckland City’s drainage system is currently combined. Without this sewer separation work, in 20 years we could see more than 2 billion litres of polluted overflows entering the harbour annually.

To learn more about what Metrowater is doing to protect Auckland City’s waterways, watch our video on Keeping our harbours clean.