The interaction of water with solid surfaces plays an important role in many chemical reactions. The present work investigates water adsorption on the clean and defective Cu2O(1 1 1) surfaces using spinpolarized density functional theory. The results show that at low water coverage, only molecular H2O chemisorption is preferred on clean Cu2O(1 1 1) surface, and the water adsorption results in surface reconstruction. Up to 1 monolayer (ML), the adsorbed H2O molecules interact with the coordinatively unsaturated Cu atoms as well as the coordinatively unsaturated surface oxygen atoms via H-bonding. Up to 2 ML, the adsorbed H2O molecules interact with the coordinatively unsaturated surface oxygen atoms and the first layer adsorbed H2O molecules via H-bonding. Ordered surface layer structures are observed at 1 and 2 ML H2O adsorption. In contrast to the clean surface, the defect surface with oxygen vacancy favors dissociative H2O adsorption with the dissociated OH group bridging the surface Cu atoms and the H atom on the coordinatively saturated third layer O atom. The adsorption mechanisms are analyzed on the basis of the total density of states. It is found that wet electron states on the clean and H2O adsorbed Cu2O(1 1 1) surfaces might be important for their photocatalytic properties. Water adsorption on Cu2O surface is stronger than on MgO, Fe3O4, Fe2O3 and CeO2, while weaker than on Al2O3. The different H2O adsorption mechanisms on different metal oxides may benefit for new H2O-splitting metal oxides catalyst designing. (C) 2015 Elsevier B.V. All rights reserved.