The struggle for drinking water in coastal areas of Bangladesh is well-documented, with the most acute crisis occurring in the southwestern coastal regions. The rainwater harvesting (RWH) system is considered an alternate drinking water option in the salinity-affected coastal regions of Bangladesh. DPHE and NGOs have undertaken various interventions regarding household RWH systems to reduce the number of people lacking improved water supply, helping to achieve SDG 6.1. Many research activities have been carried out to assess the potentiality of the RWH system in these areas, but the sustainability and long-term viability of such a system could not draw much attention. As a result, sub-optimal performance by RWH systems, both in terms of water quality and quantity, is observed in many areas. ITN-BUET undertook this research to evaluate the post-installation performance of household RWH systems in the southwestern coastal region of Bangladesh. The objective is to pinpoint essential factors governing the long-term effectiveness of the system.