Background: Harvested rainwater is one of the natural sources of water that serves as an alternative source of water supply. Due to increasing urbanization, industrialization and other developmental activities, this source of water is being polluted. The present study aimed at determining the Water Quality Index (WQI) of harvested rainwater in Owerri, Imo state, Nigeria, a growing urban city. Methods: This was achieved by collecting samples from four different (4) locations in Owerri, Imo state and subjecting the samples to standard physicochemical analysis and calculation of water quality index. Results: The WQI obtained varied across the locations. From 15.34 (poor quality) in Douglas to 188.80 in Orji to 141.20 in Imo Housing Estate and to 104.25 in Eziobodo (all excellent quality). Conclusions: The harvested rainwater of the locations sampled needs some degree of treatment before use for public health purposes including those with excellent status.