An equation of state for water is presented which accounts explicitly for repulsive, dispersive, multipolar, and association interactions. The thermodynamic properties are obtained from a simplified intermolecular potential by means of a perturbation theory, based on Wertheim’s first-order theory for associating fluids, and make use of a Stockmayer (dipolar Lennard-Jones) reference fluid. The theory is tested rigorously by comparing to it to computer simulations. Theory and simulations are found to be in general good agreement. The parameters of the theory are fitted to the vapor-liquid coexistence conditions of water. Macroscopic properties, such as the phase diagram, the vapor pressure curve, and the energy of vaporization, and molecular properties, such as the fraction of monomeric species in the saturated liquid and bonding distributions, are reasonably well represented by the resulting equation of state. Some deficiencies of the model are pin pointed, and suggestions for the development of improved potential models and/or equations of state for water are made.