This paper presents the concluding part of the study on the development cement-bonded composite tanks for rainwater storage. Water containers were fabricated using four composite mixtures (cement + sawdust, cement + sawdust + water sachets, cement + sawdust + acrylic plastic waste, and cement + sawdust + water sachet + acrylic plastic waste) and tested. The quality of the rainwater samples tested immediately after harvesting and samples stored in the composite tanks, a traditional clay pot and a plastic bucket (controls) for four and eight weeks, respectively, were analyzed. The cooling effects of the composite tanks on the stored rainwater were also investigated. Results indicated that the harvested rainwater was free of contaminants. However, there were some preliminary negative interactions between cement and the stored water. Within the first four weeks in storage, the water quality deteriorated with the pH and total suspended solids exceeding acceptable limits. A marked reduction in the salinity, total hardness, total dissolved solids, electrical conductivity, and turbidity was observed by the eighth week. Acrylic plastic waste particles generally had minimal negative interaction with the stored rainwater. The cooling effects of the tanks were positively correlated with the density and thermal conductivity of the composite materials.