The CO2 laser absorption and damage characteristics of thermal and electron beam evaporated ZnS films on Ge substrates have been investigated. The substrate temperature during deposition is shown to be an important parameter controlling film porosity and hence water ingress. The role of water is probed by a variety of techniques including laser induced desorption (mass) spectroscopy. Water is shown to lead to high film-substrate and bulk-film absorptances and to low laser damage thresholds (LDTs) with damage originating in the film. Physically dense films, which do not allow water ingress, have high LDTs limited by damage to the Ge substrates. Examination of ZnS films on Si and ZnS substrates indicates that the film absorptances and LDTs are dependent on the substrate material.