Over the past decade, approaches to improve urban water cycle management have included water-saving devices inside the home, the use of rainwater tanks, reuse of treated wastewater and water sensitive urban design (WSUD) principles to manage stormwater runoff. When several integrated water cycle management (IWCM options are implemented in unison at an allotment-scale, various levels of mains water savings, wastewater flow reductions and stormwater runoff reductions can be obtained. However, few studies in the literature have evaluated the impacts of implementing wastewater options for a non-sewered area already using rainwater tanks and onsite septic systems discharging to the environment. These scenarios are typical of peri-urban communities existing near sensitive coastal/estuarine environments. This investigation primarily reports on wastewater reuse options being introduced to a non-sewered area already using rainwater tanks and onsite septic systems. The PURRS (Probabilistic Urban Rainwater and wastewater Reuse Simulator) (Coombes, 2002) model was utilised to continuously simulate demand management (water saving devices) and the performance of rainwater harvesting and wastewater reuse to explore the reductions in rainwater tank demand, wastewater discharges and stormwater runoff that occur at an allotment-scale. This study highlights how the introduction of wastewater reuse in the study area significantly decreases wastewater flows from the allotment, increases stormwater runoff volumes from the allotment and reduces the efficacy of existing rainwater harvesting systems at the allotment-scale. Significant variations in the efficacy of rainwater harvesting were observed when increasing levels of wastewater reuse were simulated, highlighting the importance of maximising use from the rainwater tank to optimise rainwater harvesting potential, particularly in moderate to high rainfall areas. This is an important insight into the fundamental paradigm of integrated water cycle management.
Rainwater & Urban Design: 13th International Rainwater Catchment Systems Conference and 5th Water Sensitive Urban Design Conference. Proceedings of Rainwater & Urban Design 2007 (Sydney 21-23 August, 2007)