One third of the world’s population reside in water-stressed areas, and as the socio-economic impacts of climate change intensify, coastal ecosystems are particularly vulnerable. Over the last few decades, researchers and policymakers have been looking at the existing water demand–resource relationship to predict future trends and prioritize better water resource management options. This study used Water Evaluation And Planning (WEAP) to estimate future groundwater demand (domestic, agricultural, and livestock sectors) in the fragile Sundarbans ecosystem, taking into consideration different human population growth rates (high, low, and current) for the period 2011–2050. The results showed that coastal aquifer-dependent rural livelihoods are in danger of becoming unsustainable in the near future. The total groundwater demand is expected to rise by approximately 17% at the current growth rate in the study area to fulfill domestic and agricultural requirements, with an upper value of around 35% for a higher growth rate and around 4% for a lower growth rate. The impact of increasing groundwater demand was analyzed further to identify any socioeconomic shifts in this region.