Many slope stability studies have indicated that the infiltration of rainwater into a slope decreases the stability of the slope. However, the difficulty of quantifying the effect of rainwater infiltration on slope stability still exists. It would be advantageous to know what percentage of rainfall enters a slope as infiltration and how much this infiltration decreases the stability of a slope. Numerical models were used to study how infiltration into a slope varied with respect to rainfall intensity and how this infiltration affected the stability of the slope. A numerical study revealed that the amount of infiltration was highest at the crest of a slope. A case study revealed that it was difficult to quantify the amount of infiltration occurring in a slope with the numerical model. The numerical model was, however, able to illustrate the effect of infiltration on slope stability through the combined use of seepage and slope stability analyses.