Managing transboundary river basins proves a challenge for China when encountering disagreements with its neighbors that experience different political and social conditions. This paper analyzes what happens when China characterizes water as a security issue, examining China’s fluid securitization practices, where changes can be identified indicating that the Chinese government values the various water security concerns differently. Two cases are adopted for comparison. In the case of China sharing the Mekong River, the Chinese government has shown a willingness to incorporate more issues found both inside and outside of the water sector. In contrast, in the case of the sharing of the Ganges-Brahmaputra-Meghna, China’s security agenda has been limited to the consideration of water availability and has led to military security concerns. The findings indicate that China’s water security agenda is not only driven by a concern for water management over specific rivers, but also judgments that incorporate strategic military consideration with regard to countries that they are involved with. The case of China thus suggests that water security is a complex domain that demonstrates competing values and concerns in (de)politicizing water. Therefore, water-related security issues cannot be understood solely from an environmental policy perspective.