Modelling Water Distribution Strategies for a Data-Limited Small Island Using EPANET: Technical and Policy Insights from Si Chang Island, Thailand

Small islands often face chronic water shortages due to limited storage capacity, seasonal variability, and growing demand from tourism and urbanization. Si Chang Island, Thailand, experiences severe dry-season water scarcity, requiring improved water supply planning. This study applies the EPANET hydraulic modelling tool to design and evaluate water distribution networks under two scenarios: (1) a surface water supply system from the Si Chang Reservoir, and (2) a groundwater-based system near the island’s football field. Using Darcy–Weisbach head loss calculations and demand estimates, we assessed flow velocity, pressure, and construction costs. Both systems met design criteria, but the reservoir-based option achieved better cost efficiency (2.81%) and reliable pressure (minimum 15.05 m) with an average velocity of 1.20 m/s. The system can supply approximately 130% of the estimated demand, corresponding to a surplus capacity of about 30%. The findings demonstrate how hydraulic modelling can guide infrastructure planning for small, data-limited islands. Integrating technical design with policy considerations enhances the reliability, cost-effectiveness, and resilience of water supply systems. The approach presented herein offers a practical framework for decision-makers addressing water scarcity challenges on small islands worldwide.