Metrowater owns and manages the local wastewater network within Auckland City, including the Owhanake Wastewater Scheme on Waiheke Island. The network includes 1,765 km of wastewater pipes and 83 pumpstations. The waste collected by this network from around the city, with the exception of Waiheke Island, is passed to the Watercare Wastewater Treatment Plant at Mangere for processing.

Approximately 17 per cent of the drainage system in Auckland City is combined, meaning wastewater and stormwater are transported through the same pipes. Auckland City owns this combined network (332 km) and Metrowater is responsible for the maintenance and operating costs.

This combined network was designed in such a way that in times of heavy rain, when there is a lot of stormwater, the contents can overflow into waterways, resulting in a higher risk of pollution flowing into the harbours.

To address this environmental issue, Metrowater and Auckland City have given high priority to the gradual separation of the combined system into separate stormwater and wastewater networks as part of what is known as the sewer separation programme.

Failures in the wastewater system, either as a result of overflows or breaks, are a significant cause of pollution in our harbours, and Metrowater is committed to decreasing this negative impact on the environment. That is why Metrowater has active programmes in place for maintenance and replacement of assets, and to understand and address all the issues contributing to overflows.