Urban infrastructure is essential for the development of modern societies: its assessment and risk-management must be undertaken within the framework of decisions of public-interest. The fact that infrastructure is made up of networks imposes the need for a systemic approach rather than one that emphasizes individual elements. This paper proposes a hierarchical description of infrastructure systems at different levels of resolution, allowing for effective risk-assessment through the use of simplified representations of the network for the assessment of failure probability and consequences. Finally, the approach to risk-management is undertaken by means of theory of incentives.