Available fresh water resources are becoming scarce due to higher demands by industrial, recreational, municipal, and agricultural sectors. Reservoirs are one of the most efficient types of structures used to manage water resources for multiple purposes. Nevertheless, demands from individual sectors result in a variety of constraints that need to be addressed. Furthermore, socioeconomic development in reservoirs’ catchments result in potential changes in forest, agriculture and urbanisation cover which can significantly affected inflows into reservoirs. There have been a number of studies quantifying the impact of land use changes on stream flow, but few of them have considered that impact on a reservoir’s water supply. Thus, the main aim of this study is to develop a framework using a reliability-based optimisation model in conjunction with the Soil and Water Assessments Tool Plus (SWAT+) model (Arnold et al., 2012) to assess the reliability of a multi-purpose reservoir’s water supply under uncertainty in land use.