Water shortages are widely prevalent in developing countries, affecting lives of people including schoolchildren, who miss classes while fetching water for daily use. A typical case was that of Mnyundo Primary School in Tanzania, East Africa. A rainwater harvesting (RWH) system was then constructed because of easy adaptability of the technology. The purpose of this study is sustainability evaluation. The evaluation considered construction details, level of water supply service, potential for sustainability and replication. Coarse screen, first flush tank, and sedimentation tank were included for maintaining drinkable water quality through particle load reduction. The water level gauge incorporated enables easy monitoring of water usage, while the provided training and operational manual are a practical guide on system management for the users. Local labor, material and techniques used, are recommended for capacity building, sense of ownership, and cost reduction. Companies' involvement is encouraged by providing financial support to the schools as their corporate social responsibility. RWH is thus suggested as a sustainable alternative for drinking water supply.