Due to their relevance, systems such as water distribution, power grids, and gas pipelines are studied in order to guarantee robustness and security. Control systems, fault detection algorithms, and intrusion detection systems represent the crucial systems for critical infrastructure protection development. Behind each of these tools, a human operator is called to be the last decision maker in case of emergency. In this paper, a decision support system, based on the Analytic Hierarchy Process, is proposed and tested in order to suggest to the security operator the best way to recover the safe and secure state of a critical infrastructure under attack. Supported by a laboratory testbed, the behavior of a water distribution system has been emulated. A specific cyber threat has been exploited and identified to highlight the methodology designed for the decision support.