We continue a series of experiments especially designed to demonstrate the action of hydrostatic pressure on the selectivity of the cation-exchange membranes. The experimental results are explained qualitatively by the change of the interfacial transport of the ions owing to local water flows under the hydrostatic pressure action. The values of the hydrostatic pressure differences exclude the possibility of the through water flows across the membrane. We estimated the decrease in energy of activation of co-ion transition in the membrane from the side of concentration cell due to an excess of pressure in this cell.