The interface of biological molecules with inorganic surfaces has been the subject of several recent studies. Experimentally some amino acids are evidenced to play a critical role in the adhesion and selectivity on oxide surfaces; however detailed information on how the water molecules on the hydrated surface are able to mediate the adsorption is still missing. Accurate total energy ab-initio calculations based on dispersion-corrected density functional theory have been performed to investigate the adsorption of selected amino acids on the hydrated ZnO(101 ̅0) surface and the results are presented and discussed in this paper. We have also investigated the role played by water in the determination of the most energetically favourable adsorption configurations of the selected amino acids. We have found that for some amino acids the most energetically favourable configurations involve the deprotonation of the molecule if the water screening is not effective. The procedure we propose can be adopted to develop parametric models for classical molecular dynamics simulations.