The paper presents a mathematical model developed for the description of water movement in selected construction materials. In the creation of the model the Richards equation was employed that was introduced in 1931 for a homogeneous and isotropic soil medium. The equation was solved with the method of finite differences, using an explicit scheme. The experiment was conducted on a sample made of autoclaved cellular concrete in which TDR probes were placed for moisture measurement. Water movement in the sample was caused by capillary rise. Results from computer simulation were compared with those obtained in the experiment. It was demonstrated that the Richards equation can be used for the description of the dynamics of air-water conditions in cellular concrete. It was also found that differences between results obtained from the simulation and those obtained from the experiment could have been caused by the lack of calibration of the TDR apparatus that should be made individually for every medium.