We have investigated the adsorption of water on well-defined silica and silica/Pt interfaces by synchrotron X-Ray Photoelectron Spectroscopy (SXPS). For that purpose silica surfaces grown on Si have been covered with atomic platinum in order to facilitate water dissociation. Water was adsorbed from the gas phase at cryogenic temperatures and its dissociation was observed on clean and platinum coated surfaces. After desorption the adsorbed hydroxides decompose on the blank surface, whereas the hydroxides remain stable if the surface was modified with platinum. The principal reversibility of the hydroxylation process implies the necessity of point defects in order to stabilize hydroxides on well-ordered silica surfaces. Deposited platinum atoms are able to stabilize hydroxides in their proximity and act as an acceptor state on the silica surface. (C) 2016 Elsevier B.V. All rights reserved.