Electric vehicle (EV) batteries are reused in low-power demand fields such as energy storage system (ESS), even after their lifespan ends. However, the potential chances of fire may result from dependence on not employing proper thermal management for reuse modules. Therefore, this study proposes applying a water immersion system for pouch-type reuse modules. This system exhibited fire prevention capabilities during emergencies and superior thermal management performance during regular operations owing to the high thermal conductivity and specific heat of water. Particularly for pouch-type batteries, this study aims to provide insights into broadening the selection of immersion fluids, including electrically conductive substances such as water, instead of using dielectric fluids. We examined the impact on the thermal stability of the modules based on various design variables. The results showed the possibility of designing a water immersion module with an energy density of 204.2 WhL-1 by minimizing volume for thermal management purposes alone. However, a minimum 15 mm cell spacing is required to ensure the safety of thermal runaway (TR), allowing for an energy density of 179.7 WhL-1. This study anticipates the effective utilization of liquid immersion systems, prioritizing thermal stability over battery weight and volume. Particularly in ESS applications.