Floods cause damage to people, buildings and infrastructures. Due to their usual location near rivers, water utilities are particularly exposed; in case of flood, the inundation of the facility can damage equipment and cause power outages. Such impact leads to costly repairs, disruptions of service, hazardous situations for personnel and public health advisories. In this work, we present an analysis of direct and indirect damages of a drinking water supply system considering the hazard of a riverine flooding as well as the exposure and vulnerability of the system components (i.e. pipes, junctions, lifting stations etc.). The method is based on the combination of a flood model and an EPANET-based piping network model implementing Pressure-Driven Demand, which is more appropriate when modeling water distribution networks with many off-line nodes. The two models are linked by a semi-automated GIS procedure. The evaluation of flood impact on the aqueduct network is carried out for flood scenarios with assigned recurrence intervals. Vulnerable elements exposed to the flood are identified and analyzed in order to determine their residual functionality and simulate failure scenarios. Impact metrics are defined to measure service outage and potential pipe contamination. The method is applied to the water supply system of the city of Florence (Italy), serving approximately 385 000 inhabitants. Results show that for the worst failure scenario 420 km of pipeworks would require flushing and disinfection with an estimated cost of 21 Mio €, which is about 0.5 % of the direct flood losses evaluated for buildings and contents.