The need for a simple model for the dissolution of glass in water which is easy to evaluate numerically is discussed. An approximate solution is obtained for a model in which the glass-water interface is assumed to corrode with constant velocity and diffusion of the leached cation to the interface is balanced by the diffusion of hydrogen ions inward from the water. The relation of this model to previous models is indicated and its applications and limitations are briefly discussed. The need to extend this model to include glasses with several leachable cations is noted in connection with glasses for the containment of nuclear waste.