Water diffusion into silica glass results in a thin zone near the surface of the glass. In this zone the water reacts with the SiO2 structure and “damages” the originally intact SiO2 rings. The consequence is a reduced Young’s module. This effect can be described by use of continuum damage mechanics according to Kachanov  and Lemaitre . In this paper the dependency between hydroxyl concentration and damage will be described for large water concentrations by using the pore models of Wang  and Phani and Niogy . As an application, the hydroxyl concentration at crack tips is computed and crack-tip stress intensity factor is estimated.