The adsorption of water on the polar Cu2O(100) surface has been studied theoretically. Both molecular and dissociative adsorption are studied. Dissociative adsorption is found to be energetically favorable, and good qualitative agreement is achieved between experimental and simulated UPS spectra for low coverages. The simulated spectrum allows for an assignment of the peaks in the experimental spectra. For higher coverages the model used is found to be insufficient; we believe the main reason for this is adsorbate-induced reconstruction of the surface.