In this study, the emergency water supply capacity of the Shepan Island in Ningbo City was estimated based on comprehensive evaluation of the freshwater resources on this island. A groundwater numerical model was established to predict the groundwater level recovery capabilities in emergency exploitation conditions. In addition, the environmental effects such as groundwater depression cones, land subsidence, and saltwater intrusion were evaluated. The results show that it is feasible to construct the emergency water source area on the Shepan Island. This study provides a basis for further exploration of emergency water sources in the area.