Rainwater is considered as the cleanest source of water in the world, however, its utilization in the Philippines was only limited to non-potable purposes. Previous studies claimed that rainwater can be a viable source of potable water if treated accordingly and can serve as an aid to the centralized water distributor in the community, thus, with the impending problems concerning water scarcity, there is a need to develop rainwater harvesting system that can produce potable water. This study was conducted to propose a design of rainwater harvesting system filtration for an alternative potable water source and to assess the physicochemical properties of the harvested rainwater before and after filtration. This study utilized a descriptive-developmental research design using researchers-made questionnaire subjected to validation by six (6) experts as a measurement for the evaluation of the acceptability level of the design with civil engineers and mechanical engineers as expert participants. Also, a physicochemical analysis was conducted based on the Philippine National Standards for Drinking Water 2017, Annex B-1 Mandatory Drinking-Water Quality Parameters. The result showed that the filtered rainwater complied with the required standards stipulated in the Philippine National Standards for Drinking Water (PNSDW 2017). This implies that rainwater is a viable source of drinking-quality water using a system with the purpose of capturing, storing, and treating rainwater. Also, the expert participants evaluated the proposed design as acceptable in terms of its functionality, durability, and usability. Hence, it is recommended that the proposed design may be considered for utilization as an alternative source for potable water.