Two approximate methods for the water transport number evaluation in ion-exchange membranes (IEM) are proposed. The first one allows the evaluation from the electrical conductivity, diffusion permeability and emf apparent transport number. It can be considered as a method for complementary IEM characterisation. The second demands only the knowledge of the emf apparent transport number and gives sufficiently approximate values. Experimental data on the water transport numbers for MK-40 in KCl and CM2 in KCl, NaCl and LiCl solutions are presented and the mechanism of the water transport is discussed. (C) 2004 Elsevier Ltd. All rights reserved.