A first principles simulation study of the H-terminated InP(100)-water interface is presented with an aim to understand the electronic structure of the interface. The simulation has been carried out using the ab initio Car-Parrinello molecular dynamics method within a pseudopotential formalism and the Becke-Lee-Yang-Parr generalized gradient approximation to the exchange-correlation potential. Dissociative adsorption of H2O molecules onto H/InP(100) surfaces, leading to formation of In-OH and In-H bonds on the (100) surface, occurs at the interface, in a manner similar to the experimentally demonstrated dissociative adsorption of H2O onto n-InP(110) surface. This process indicates a very strong coupling between the semiconductor and the water states. Also, simulation carried out for two H/InP(100) surfaces reveal that more H2O dissociations occur near the rougher atomically corrugated surface, in accordance with observations from experimental studies designed to determine the morphological influences on H2O dissociation near semiconductor surfaces. An analysis of the electronic structure of the interface further reveals the charge density profile of the H/InP(100) surface states to be strongly influenced by the water states, especially those arising from the first overlayer. Additionally, the net charge of the solvated H/InP(100) slab is found to be positive and the net atomic charges on the chemisorbed H atoms are found to be negative, indicating a charge transfer, particularly, from the surface-In atoms to the chemisorbed H atoms.