Water was selectively separated from water/He, water/HC and water/HC/He mixtures (HC being methane, propane or n-butane) using mordenite/ZSM-5/chabazite and ZSM-5 membranes. The membranes were prepared on both alumina and stainless steel tubular porous supports by in situ liquid phase hydrothermal synthesis. Water permeated faster because its preferential adsorption on the pores of the hydrophilic zeolite membranes; furthermore, capillary condensation in microporous defects between zeolite crystals is also possible under the experimental conditions used. The influence of the nature of the hydrocarbon in the mixtures and of the operating conditions (temperature and feed composition) on the separation performance of the zeolite membranes was analyzed. (C) 2000 Elsevier Science B.V. All rights reserved.