The development of a generalised equation for the annual water savings through rainwater tanks under different climatic conditions for southwest Brisbane (Australia)

Optimisation of rainwater tank outcomes has been a challenge for the users, as the water savings and reliability depend on many factors such as rainfall amount, rainfall distribution, tank size, roof area and rainwater demand. Among the analysis methods, daily water balance modelling is the most reasonable and acceptable approach. However, general end-users can hardly interpret/grasp the outcomes of such analyses. To overcome this hurdle, this paper presents the development of a generalised equation for calculating expected water savings through rainwater tanks with major contributing factors like rainfall, rainwater demand, tank size and roof area for southwest Brisbane (Australia). Daily rainfall data was collected for the station, Oxley which is in southwest Brisbane from the Australian Bureau of Meteorology website. The expected annual water savings for different combinations of rainfall, tank size, roof area and demand are presented in the form of charts that were converted to a generalized equation having independent variables of rainfall, tank size, roof area and demand. Results from the developed equation were seen matching with the model (eTank) simulated results. Such an equation can be easily incorporated into mobile apps or computer programs to help quick calculations for expected water savings.