The model of water adsorption on carbons proposed five years ago by Do and Do is analyzed and improved. Following the experimental evidence that for activated carbons surface active groups differ in the value of the energy of interaction with water molecules, we propose to extend the original model to take this fundamental feature into account. For the original DD model, as well as proposed new heterogeneous one (HDDM), we develop also the corresponding isosteric enthalpy of adsorption formulas. The features of the HDDM are studied via simulations. It is shown that the new model predicts the shapes of adsorption isotherm as well as corresponding enthalpy observed for real experimental systems. Finally, the HDDM is successfully applied to description of arbitrarily chosen adsorption and enthalpy of adsorption data. Up to our knowledge, HDDM is the first model describing satisfactorily water adsorption isotherms and corresponding enthalpy data measured on different microporous activated carbons in the whole relative pressure range. (c) 2005 Published by Elsevier Inc.