Water supply systems are exposed to events that affect the normal service provision. Water companies should follow their own policy rules to manage and overcome these types of threats. In this article, resilience is identified as the capacities of the system to delimit the impacts of hazardous event, which may be characterized by its severity and duration. The effects of disruptive events to the water service delivery are classified into water scarcity, discontinuity of water supply, discontinuity of hydraulic conditions and discontinuity of drinking water quality. The loss of service level is established by failure thresholds named as a standard level, a normative level, an accepted level and a critical level. These thresholds allow formulating management actions at different stages to reach the standard level of service that identifies when the systems returns to normal conditions. The global model defined by the loss of service and time is used to measure resilience by means of a resilience factor. It depends on each type of defined threat and considers the mentioned failure thresholds. The methodology is applied to a complex real-life system, managed by Canal de Isabel II Gestión (Spain) for different study cases: a drought, pipe breaks and events that affect the water quality conditions. Real data allow contrasting the protocols of management established by the water company. The methodology helps water utilities update their protocols for a certain hazard and provide useful information to plan their investments in order to improve the system resilience.