The water vapor sorption capacity and corresponding generated heat amount are the most important properties for adsorbents in thermochemical heat storage systems. In order to understand the adsorption/desorption behavior of three nanoporous molecular sieves such as 5A, mordenite and natural clinoptilolite (with different structures, Si/Al ratios and balancing cations), the pure zeolites and their composites (obtained by depositing NaOH onto the molecular sieves) were characterized in their structural and surface properties by using appropriate techniques (N-2 adsorption isotherms at -196 degrees C, XRD and (MAS) NMR). The adsorption of water was performed using a Setaram TG-DSC 111 apparatus. Three successive cycles of hydration (at 20 degrees C)/dehydration (at 150 degrees C) were carried out to check the stability of the system in conditions close to those used in adsorption heat pumps. The measured heats of dehydration vary in the 183-614kJkg(sample)(-1) range for the various samples that present also different water vapor sorption capacities (from approximate to 0.08 to approximate to 0.14 kg(H2O) kg(sample)(-1)). The water adsorption/desorption behavior of the zeolites was mainly related to the porous structure and to the Si/Al ratio, that drive the affinity of zeolite to water. The experimental results showed that the impregnation of the three kinds of nanoporous zeolites with different amounts of sodium hydroxide negatively affects the sorption characteristics of the composites. The blockage of zeolite pores (that limits the access to water molecules), the slight amorphization of the zeolite structure and the formation of carbonates are some of the phenomena identified to influence the water sorption onto NaOH-containing composites. Copyright (c) 2016 John Wiley & Sons, Ltd.