Wastewater from private residences and non-domestic sites goes into the wastewater network and is pumped to treatment plants for treatment and disposal. The wastewater network in this local board area is extensive and spread over the Lower Tamaki River, Upper Tamaki River, Māngere and Onehunga catchment areas. There are broadly two main wastewater areas. Firstly, Glen Innes, Tāmaki, Panmure and Mt Wellington feed into the Eastern Interceptor from Glendowie and Mt Wellington. This line travels south through Westfield and onto the Māngere Wastewater Treatment Plant. Secondly, Penrose, One Tree Hill, Southdown and Onehunga feed along the Onehunga and Royal Oak lines into the Western Interceptor and into the Māngere wastewater treatment plant.
There are several upgrades to the local wastewater network that are taking place, including the Dunkirk wastewater pump station
and pipeline replacement, and the Glen Innes pump station
Drinking water for Glen Innes, Tamaki, Panmure, Mt Wellington and Sylvia Park primarily come via the main water treatment plants at Ardmore, Waikato, Waitākere and Huia. Water reservoirs are placed along the network, namely at Mt Wellington and St Johns, to ensure supply during times of peak demand and smooth flows during the day. For the Onehunga, Penrose, and Southdown areas, drinking water comes via the Onehunga water treatment plant which draws from an underground aquifer. Situated within One Tree Hill Domain are the significant One Tree Hill, Onehunga High, Onehunga Low and Campbell Road reservoirs.