Water was diffused into very dry thermal SiO2 films under conditions such that the penetration of water related electron trapping centers was of the order of the oxide thickness. In both dry oxides and water diffused oxides, production of negative bulk oxide charge Qot and positive interface charge Qit by an avalanche-injected electron flux was observed. The efficiencies of both processes were enhanced by water indiffusion. Analysis of the kinetics of charge generation indicated that production of trapped electron centers (Qot) was required for subsequent production of interface states and charge (Qit). Models for both processes are discussed. We suggest that inelastic collisions of conduction electrons with the trapped electron centers releases mobile hydrogen atoms or excitons. The mobile species migrate to the Si-SiO2 interface and form states and fixed charge.