The most frequently used approach to the description of liquid transfer in porous media is based on its analogy with the diffusion process. It introduces effective diffusivity D(u) depending on actual moisture content u. On the basis of experimental data obtained by means of neutron radiography, it is shown that this function D(u) cannot be regarded as a material characteristic because of its strong dependence on initial and/or boundary conditions. Alternative possibilities of the moisture transport description are discussed.