The goal of this paper is confined to the derivation of an equation for the analysis of the phenomenon of water flows along an asphalt pavement. By referring to the general theory for the percolation of water in rigid porous materials, we propose the theoretical derivation of models for some tests on asphalts. In order to validate the formalized models and to analyze the relationships among the main indicators introduced, in-field experiments were designed and performed. As our main results, we develop a model for tests on asphalts and validate it partially by means of our experimental results.