In the present study, the hydrodynamic force affected by a lapping wave induced by supplied falling water acting on the vertical wall of a portable water storage tank was analyzed using a nonlinear Peregrine model. The lapping wave's maximum run-up amplitudes and the hydrodynamic forces in the wall of the tank measured by linear and nonlinear Peregrine's models were compared numerically. As a result, it was concluded that the linear model may underestimate the effects on the vertical wall; therefore, it is more appropriate to use a nonlinear Peregrine model. Furthermore, this result can contribute to the stable structural designs of portable water storage tanks.