Domestic wastewater is derived from bathrooms, kitchens, laundries and toilets. It includes human waste (containing pathogens), paper, soap, detergent residues and food scraps.

Effective treatment and management of this wastewater is necessary to protect public health and the environment. It is treated either through discharge to a reticulated sewerage system or to an individual onsite wastewater system—most commonly a septic tank.

In the 1950s, metropolitan Melbourne grew rapidly, particularly in the eastern and southern suburbs, but the provision of sewerage infrastructure did not keep up. To overcome this, councils approved the use of onsite wastewater treatment systems to manage wastewater and allow development to proceed. These properties were placed onto backlog programs, to gradually connect to the reticulated sewer network. A significant number of these properties are found on the Mornington Peninsula and in the Yarra Ranges. Today, South East Water Ltd. (SEW) and Yarra Valley Water Ltd. (YVW) run the two metropolitan backlog programs in Melbourne.

In this audit we examined whether the environmental and public health impacts of domestic wastewater are being effectively managed. We examined SEW and YVW, Yarra Ranges Council (YRC) and Mornington Peninsula Shire Council (MPSC), and the Department of Environment, Land, Water and Planning (DELWP) and the Environment Protection Authority (EPA).

We looked at the efficiency, economy and effectiveness of water authorities’ sewer backlog programs, the extent to which councils are managing the risks on onsite domestic wastewater and the regulatory system and whether its implementation supports water authorities and councils in protecting the environment and public health.

We made 8 recommendations for DELWP and EPA, 4 recommendations for MPSC and YRC and 3 recommendations for both YVW and SEW. We made two further recommendations for YVW and one recommendation for YRC.