Recent catastrophic events such as Hurricane Katrina have highlighted the importance of interdependency to result in cascading effect among critical infrastructures. Previous studies investigated and categorized the interdependency of critical infrastructures based on qualitative consideration and case studies. However, it is still necessary to approach this quantitatively. The main purpose of this study is to model the behavior of interdependent infrastructures in urban systems, especially water and energy supply, and suggest management policy for water supply systems to increase its resilience. The relationship between two infrastructures was converted into causal loop diagrams. The system dynamics model considering the interdependency was developed with components and relationship from previous research. The capacity of water supply system and its recovery capacity under disruptive scenarios was assessed as the resilience of the water supply system. The simulation result showed that the order of interdependency has high sensitivity with the variance of resilience. It was also found that enhancing the resilience of the water supply system improved not only the recovery capacity of the water supply system but also of the energy supply system. The most efficient policy leverage was found in the enhancing feedback loop of resource exchange between two infrastructures. Some assumptions in the relationship between components should be formulated with more concrete observation and mathematical consideration in further studies.