Rooftop Rainwater Harvesting (RWH) systems are critical interventions for addressing water scarcity in climate-vulnerable, water-stressed regions. In Sri Lanka’s dry zone, these systems have been promoted for over two decades to support communities facing seasonal droughts and limited access to surface water. This study evaluates the performance and socio-environmental impact of RWH systems in the Polpithigama Division, Kurunegala District, focusing on system configurations, water security contributions, and spatial priority mapping. […] These findings highlight the role of RWH systems in enhancing climate resilience and contributing to Sustainable Development Goal 6 (Clean Water and Sanitation).