This study aims to provide a simplified approach to investigate the influence of the immersed water depth on a bridge’s seismic performance. Due to the service life of an infrastructure is often long, it is important to realize the seismic performance in its life. However, there are tens of thousands of bridges in Taiwan and therefore, an easy but accurate analysis approach is needed. A case study is conducted to illustrate the proposed methodology and the structural performances with added mass are investigated to show the submerged water effect. The structural performance is measured by the displacement ductility during seismic excitation. According to the results obtained, highly variability of seismic performances is observed and it is important to include the immersed water depth to capture the seismic capacity of a bridge.