A more than 150 years old, seven span masonry arch bridge, part of “Cavour channel”, spanning over torrent Cervo in Piedmont (Italy), was hit by a flood during an extreme rain event in 2020. An intermediate pier has suffered a massive settlement of the foundation, with displacement and rotation components, so to induce near collapse in the masonry arches and extensive damage to the upper masonry water channel. A performance-based approach was developed for the assessment and the strengthening of the masonry bridge, considering the complex structure comprising arches and upper massive channel. Soil-structure interaction and water-channel interaction are accounted for in the seismic appraisal, completed by a limit capacity assessment of the main arches through an incremental static analysis. The results of these investigations allow increasing the service life of the bridge, delivering for the first time the seismic risk assessment of a critical water infrastructure that for more than 150 years has played a central role in the economy of northern Italy.