Contamination of a public water supply distribution system would have far-raging public health and economic effects. Emergency response decision-makers need a tool for quickly calculating resources requirement in the aftermath of a contamination incident. A model is needed to describe the potable water distribution system itself and the cascading effects of a disruption of that distribution system on other public institutions such as hospitals, transportation networks, etc. In this paper we present a system dynamics model describing a potable water distribution system that serves an urban area. This model is a component of the Critical Infrastructure Protection Decision Support System (CIP-DSS) project, which models the dynamics of a set of coupled individual infrastructures. We investigate the interdependencies of potable water distribution systems on other critical infrastructures merging our model with other infrastructure models developed under the CIP-DSS project. The main focus of this work is to study the consequences of a disruption on a potable water distribution system. For this purpose we analyze the effects on public health and the economic consequences resulting from contamination of a public water supply.