Ab initio density functional theory has been used to investigate the effects of surface charge on adsorption and dissociation of H2O on the Cu(111) surface. The adsorption energies at all high symmetry adsorption sites are similar on the negatively charged surface, indicating that there is no preferable adsorption site. While on the positively charged surface, H2O molecule on the atop site has the strongest adsorption among all adsorption sites. We also show that changes in the surface charge can significantly alter the activation energy of dissociation as well as the mechanism selectivity.