Centralised and decentralised water infrastructure: the best of both worlds

Over the past 100 years, the procurement of Australian water and wastewater infrastructure has been guided by centralised philosophies. Centralised philosophies describe the water trinity of potable supply, sewerage services and stormwater management. However in recent years it has become clear that this approach is not economically, socially or environmentally sustainable in its current form. Decentralised solutions such as rainwater tanks, wastewater treatment and reuse and water sensitive urban design (WSUD) have been shown to provide significant benefits that compliment the current centralised approach. The aim of this paper is to highlight the comparative mains water savings, and reductions in wastewater flows and stormwater runoff at the allotment scale, with respect to centralised and decentralised water infrastructure approaches. The Probabilistic Urban Rainfall and Wastewater Reuse Simulator (PURRS) (Coombes, 2002) was used to simulate allotment scenarios based on 1 to 5 people households and 150, 200 and 300 m2 roof areas for Sydney, Brisbane and Melbourne. Results show significant mains water savings and wastewater flow and stormwater runoff reductions at the allotment scale can be obtained from decentralised options and one must question our insistence on the current centralised approach. Decentralised options are rarely considered by water authorities or government planners because they are skeptical on the benefits they provide. This skepticism may have an ulterior motive that will be a challenge to address. The centralised philosophy appears to be a function of the current vested interests in centralised management of water supplies, dividend returns to government from the sale of water and consultants that are dependent on the current centralised governance structure. This approach has led us away from sustainable water management over the past 100 years and unless decentralised alternatives are embraced and included within the future development of Australia’s water infrastructure we will continue to place greater burdens on existing water supply catchments and remain susceptible to water shortages into the future.