Evaluation of the impact of rainwater tanks on the performance of stormwater management systems is reliant on understanding of the storage volumes available in tanks prior to storm events of a given average recurrence interval (ARI). This study has used continuous simulation, historical rainfall sequences and a unique method utilising virtual storages to determine storage volumes available in rainwater tanks prior to rain events of a given ARI. Available storage volumes in rainwater tanks prior to rain events at each location were observed to (i) increase with tank capacity, household size and the ARI of rain events, and (ii) decrease with increases in connected roof areas at Adelaide, Brisbane, Melbourne and Sydney. The variation in these parameters was observed to be conditioned on local climate and water demand patterns. The optimum use of rainwater tanks as part of a stormwater management strategy will be dependent on careful consideration of the key variables; local climate and water use patterns, the selected end use of rainwater, tank size and roof area.
