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Among the alternative water sources, rainwater harvesting is the most popular and readily useable. However, studies related to the knowledge of future sustainability of this resource and its usage are limited. In this paper, projected future rainfall data for two distinct future set of periods (2020–39 and 2080–99) are used to calculate future water savings potentials using an earlier developed daily water balance model for five different regions in Sydney, the largest city in Australia. The rainfall data is collected from four different projection tools provided by the Australian government's climate data portal. With the assumptions of average household water demand as 400 L/day, a tank size of 5000 L and a roof catchment area of 200 m2, water savings and reliabilities of water availability are calculated for future scenarios for five different locations within a broader region of Sydney. Water savings and reliabilities are then compared with the same for current average rainfall condition based on historical data for the same locations. It is found that for most of the studied cases, both in the near (2020–39) and distant (2080–99) future, water savings as well as reliabilities are expected to be decreased compared to the current average scenario. However, in the distant future, both water savings and reliabilities are expected to be increased compared to the near future scenario. Also, it is predicted that spatial variability of water savings within the selected region will increase compared to the current scenario. [ABSTRACT FROM AUTHOR]