There are debates about whether rainwater is suitable as drinking water. A serious shortcoming of the debate is that there are differences in the design and management of rainwater harvesting (RWH) systems. This study is based on the performance of two RWH systems that are used for drinking purposes at a kindergarten and a primary school in Cu Khe, Vietnam. Each system comprised a painted galvanized iron roof, a first-flush diverter, two stainless steel tanks connected in series, a calmed inlet, mosquito screens on open holes, PVC pipelines, filter cartridges, and a UV sterilizer. During 18 months, stored rainwater was sampled five times, and treated rainwater was sampled four times. Twenty-three water quality parameters were analyzed, including pH, total dissolved solids, turbidity, nitrate, nitrite, ammonia, hardness, arsenic, iron, cadmium, nickel, chromium, manganese, mercury, selenium, lead, zinc, Escherichia coli, and total coliform. It was found that all the physicochemical qualities of the stored rainwater, prior to treatment, satisfied the World Health Organization (WHO) drinking water guidelines. After physical filtration and UV sterilization, all parameters, including microbiological indicators, satisfied the WHO drinking water guidelines. Further management strategies to stabilize water quality were discussed.