The current status of the exploitation, use, and management of water resources in the context of socioeconomic development, climate change, and issues related to the region are causing negative impacts on the water resources of Vietnam. This study aimed to develop a framework for assessing Vietnam’s water security based on the following key aspects: (i) the availability of water resources; (ii) the current status of water exploitation and use; (iii) the current status of waste water and water pollution; (iv) water resource management organization; and (v) water-related disasters, including floods, droughts, subsidence, coastal erosion, landslides, ecological imbalance, and diseases related to water resources. In particular, the challenges of transboundary water resources and the food–energy–water nexus were investigated. We reviewed the assessment frameworks that have recently been developed outside Vietnam or regions with similar climates and analyzed the characteristics of downstream and rapid-growth countries such as Vietnam using a number of key water resource indicators, both qualitative and quantitative. From these processes, we developed an assessment framework and provided a perspective on water security. The results of this study showed that the challenge of transboundary water resources, the impact of climate change, the pressure on socioeconomic development, and the water–energy–food nexus are core issues that need to be addressed from the perspective of water security in Vietnam. This case study may be helpful for downstream and developing countries.