Framework for Enhancing the Supply-Demand Balance of a Tri-Supply Urban Water Scheme in Australia

Fit-for-purpose potable source substitution of appropriate water end uses with rainwater or recycled water is often essential to maintain water security in growing urban regions. This paper provides the results of a detailed supply-demand forecasting review of a unique tri-supply (i.e., potable, A+ recycled and rain water sources reticulated to household) urban water scheme located in Queensland, Australia. Despite the numerous benefits of this scheme, system efficiency (e.g., reduced demand levels, water treatment, low chemical and energy use) and economic viability (i.e., capital and operating costs per kL of supply) aspects need to be considered against derived potable water savings. The review underpinned the design of a framework to enhance the schemes supply-demand balance and reduce the unit cost of alternative source supplies. Detailed scenario and sensitivity analysis identified the possibility of a refined scheme design, whereby the A+ recycled water supply would be reticulated to the cold water input tap to the washing machine, and the rain tank that originally supplied this end use be removed from future constructed households. The refined scheme design enhances the present recycled plant utilisation rate and reduces the cost to home owners when building their dwelling due to the removed requirement to install a rain tank to indoor end uses; such actions reduce the overall unit cost of the scheme.