The work presents the results of estimation of free water transport numbers through the ion-exchange membrane using the Stern double electric layer theory and physicochemical and structural characteristics of the membrane, if the ion-exchange membrane is presented as a capillary system. A good agreement between the experimental data and the results of calculations in frames of the model for alkaline metals chlorides solutions with concentration >= 1 mol/L was observed, that is practically important for electrodialysis concentrating of salt solutions. A significant influence of the polymer matrix nature on the fraction of the through mesopores has been revealed. The applicability of this model approach to the description of electroosmotic transport of free solvent through modified membranes was shown.