With escalating global freshwater scarcity, the Mekong Delta basin has emerged as one of the most socially and ecologically vulnerable regions, experiencing severe freshwater stress and storage loss. This vulnerability is primarily driven by the progressive "loss of land and freshwater" phenomenon, which encompasses a range of interconnected environmental issues, including land subsidence and seawater intrusion. The exponential growth in population, urbanization, climate change and rapid industrial and agricultural development has significantly increased the demand for freshwater, placing already limited supplies under immense pressure. In the coastal zones of the Mekong Delta, groundwater has become the primary and increasingly overexploited source of freshwater. Consequently, a decline in hydraulic heads and the threat of saline intrusion have become pressing concerns. To gain a comprehensive understanding of the hydrogeochemical processes at play, a meticulous investigation was conducted in the coastal province of Ca Mau, Vietnam. Through extensive sampling campaigns and rigorous hydrogeochemical analysis, this study sheds light on the intricate dynamics of groundwater chemistry in the region. The results reveal that ion-exchange processes and the decomposition of organic matter play dominant roles in shaping the groundwater chemistry. These findings hold significant implications for the sustainable management of water resources in the Mekong Delta. By unraveling the past and current hydrogeochemical groundwater dynamics, stakeholders can develop effective strategies to mitigate freshwater scarcity. The knowledge gained from this research contributes to the scientific understanding of hydrological systems and aids in the formulation of integrated water management policies for the region's long-term sustainability.