Unplanned urban expansion, which disregards urban runoff drainage, leads to flooding in urbanized catchments, making it one of the most dangerous disasters. The current study aims to evaluate the effect of implementing active rainwater harvesting (RWH) tanks at a domestic scale in controlling and managing urban floods in a semi-arid urban area. The study employed PCSWMM, the Personal Computer Storm Water Management Model, to run a 2D model for investigating the effect of implementing RWH tanks on peak runoff reduction. Simulations were conducted for various return periods (2y, 5y, 10y, 25y, 50y, and 100y) for both with and without RWH scenarios, utilizing varying tank sizes. The research found that domestic rainwater harvesting has a major effect on reducing surface runoff. The reduction values are dependent on the depth of the rainfall, the size of the tank, and the proportion of the roof ar-ea to the total area of the parcel. Moreover, the reduction values have maximum values which cannot be exceeded even with increasing tank size. The maximum peak reduction values are (42.37%, 40.43%, 39.65%, 38.65%, 38.2%, and 37.75%) for the return periods (2y, 5y, 10y, 25y, 50y, and 100y) by using tank sizes of (8, 12, 18, 24, 32, and 40) m3 respectively. Gener-ally, the deduced results improve understanding of the active domestic rainwater harvesting effect on the runoff peak reduction in a semi-arid urban area and its ability to reduce urban flood depths and discharges.