We report studies of water-silica surface interactions using a hybrid first-principles-classical molecular dynamics simulation method. The quantum region, which is treated with high accuracy density functional theory, is embedded in a large amorphous matrix described by classical potentials. With this model, both nondissociative and dissociative processes of water molecules at a two-membered ring site, which has been found experimentally on the surface, are studied. Our investigations provide qualitative and quantitative descriptions of the reaction pathways and energy landscape. A barrier-free double hydrogen atom transfer process is observed. (C) 2003 American Institute of Physics.