The structure and properties of an atom-based model of water next to a planar interface are solved using an approximate integral equation theory. The input to the calculations is the structure of the bulk water in the form of the direct correlation functions. Predictions from the theory include the oxygen and hydrogen density profiles perpendicular to the interface, the mean electrostatic potential, the potential of zero charge, and the differential capacitance. The predicted structure is relatively insensitive to both the surface potential and the details of the short-range wall-water potentials, and exhibits a layered structure which extends approximately 15 Angstrom A into the liquid. For our initial choice of the short-range wall-water potential, we predict a value of -32 mV for the potential of zero charge and a differential capacitance of 4.89 mu F cm(-2) for pure water at a planar interface. The capacitance is apparently independent of the surface charge density and the surface potential.