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The evaporation loss is a key component that affects managing the water resources of arid and semi-arid regions, where the resources are not uniformly distributed. Due to the climate condition and the physical characteristics of arid regions, a major proportion of precipitation is often unavailable through the flash floods, while merely a small fraction recharges the groundwater aquifers. Therefore, to achieve sustainable development, managing the water resources based on rainwater harvesting systems is inevitable. The main aim of this study was to assess the reliability of the rainwater harvesting systems designed for a future period (2017-2030). Thus, monthly climate data (e.g., precipitation) were simulated by using the outputs of general circulation models (GCMs) of the newest generation in the coupled model intercomparison project phase 5 (CMIP5) as the first step under two representative concentration pathways (RCPs), i.e., RCP2.6 and RCP8.5. Then, the data were downscaled spatially through bias-correction spatial disaggregation (BCSD) method for 20 grid points surrounding Birjand rain gauge station, east of Iran. Monthly precipitation of Birjand rain gauge station was interpolated automatically by means of the ordinary Kriging method during a future period, between 2017 until 2030. Data pre-processing in geostatistical methods, including investigating the normality, isotropic, trend analysis, and semi-variogram selection, was also carried out automatically through coding in MATLAB. Finally, using the interpolated monthly precipitation time series, the reliability of the precipitation harvesting systems was assessed for a different range of rooftop areas and storage tank capacities. Results indicated that this process can meet a significant volume of the household non-potable water demand by RWHS. Similar reliability values based on the projected monthly precipitation due to two GCMs and two RCPs were extracted for future period. The reliability of RWHS acquired by RCP2.6 will not widely diverse from RCP8.5. Totally, for semi-arid region, it is possible to supply about 20% of non-potable water demand in the future periods. Although this amount seems to be a low value, it should be noted that RWHS may prevent extra groundwater withdrawal and thus enhance the sustainability of the water resources.