We present a density functional theory study of water adsorption on K1-yNayTa1-xNbxO3 (KNTN) surface terminations. The adsorption configuration and energy are determined and the bond formation between water molecule and KNTN surface are investigated by analysis of difference electron density and partial density of states. Our calculations reveal that the energetically favorable configurations for water monomer adsorption is at the K-Na bridge site on the K(Na)O-termination and the Nb top site on the Ta(Nb)O-2-termination. With the coverage increasing, the water-surface interaction per water molecule decreases because of the formation of interwater hydrogen bonds, whereas the surface geometry becomes more roughness. The variation of bandgap for water adsorbed KNTN surface is also studied. We find that the interaction between water and surface would lead to a bandgap increase of KNTN surface, which is correlated to the electrons density redistribution. (C) 2014 Elsevier B.V. All rights reserved.