As an alternative and sustainable source of water, rainwater harvesting (RWH) has been studied extensively around the world in recent times. Climate change may bring significant changes in rainfall pattern. In this study, 60 years historical rainfall was evaluated. Frequency analysis for rainfall events and dry day duration was carried out to produce exceedance probability curves. Notable change in rainfall pattern occurred for 10th percentile exceedance probability for the decades 1976-1985, and 2006-2015, from 41mm to 46mm (+12.2%), and from 44.5 mm to 40.1 mm (-9.9%) respectively. Change in dry day duration was insignificant. A software was developed in MATLAB to simulate the daily water balance model for determining reliability, volumetric reliability and water saving potential of the RWH systems. Analysis showed highest reliability in the 1976-1985 decade at 8.2%-3.4%, gradually decreasing to lowest during 2006-2015 at 6.4%-2.4%, depending on catchment and water demand scenario. Volumetric reliability was highest at 15.5%-10% for the decade 1976-1985, gradually falling to 13%-8.5% at 2006-2015. For water saving potential, 1955-1964 was treated as baseline. 1976-1985 showed the highest increase in water savings potential at (+11.5% ~ +11.9%), gradually decreasing to (-4.5% ~ -5.1%) during 2006-2015. Changes for reliability and volumetric reliability are not major, but still noticeably reduced in the recent decade. Effect on water saving potential is more prominent possibly indicating significant negative impacts of climate change on RWH systems in Dhaka city.