Recently, a new mechanism for the stabilization of the polar surfaces of ZnO has been proposed. This mechanism involves the transfer of electrons between the (0001) and (000 (1) over bar) surface. In the current study an alternative mechanism involving the adsorption of water onto the polar surfaces has been investigated using ab initio all electron, hybrid density-functional theory. On the basis of the current study, such a stabilization mechanism can be ruled out at low-temperatures and low-partial pressure of water. In addition, we present evidence that the ZnO(000 (1) over bar)-O surface may be a gas sensor for hydrogen.