Abstract: Water is a scarce resource in arid regions, and hence water harvesting is critically important in these regions for which many different means are adopted including groundwater and rainwater harvesting. This paper examines the feasibility of rainwater harvesting from roof catchments in arid regions of Australia. For this, ten representative locations in the arid regions of Australia are selected. Also, ten different sizes of rainwater tanks ranging from 5 kL to 50 kL and three different combinations of water uses are considered. A model is developed to simulate the performance of a rainwater harvesting (RWH) system. It is found that the reliability of a RWH system is highly dependent on mean annual rainfall at the location of interest. It is found that a 20 kL tank can provide a reliability of 61%–97% for toilet and laundry use depending on the location within the Australian arid regions. At the current water price, RWH system is not financially viable in the Australian arid regions. The methodology adopted in this paper can be adapted to other similar arid regions of the world.