Electrical water heaters (EWHs) are important candidates to provide demand-response services. The traditional optimization method for EWHs focuses on the optimization of the electricity consumption, without considering the shifting potential of the water-use activities. This paper proposes an optimization method for EWHs considering the shifting potentials of both the electricity consumption and water-use activities. Considering that the water-use activities could be monolithically shifted, the shifting model of the water-use activities was developed. In addition to the thermodynamic model of the EWH, the optimal scheduling model of the EWH was developed and solved using mixed-integer linear programming. Case studies were performed on a single EWH and aggregate EWHs, demonstrating that the proposed method can shift the water-use activities and therefore increase the load-shifting potential of the EWHs.