An analytical form for the equation of state of water in the region 0.5–300 kbar is presented. The functional form of the equation was first proposed by Born to characterize the melting of crystalline solids, and is applied to water in the thermodynamic vicinity of the Hugoniot. The derived equation is equivalent to the Mie‐Gru¨neisen equation of state if the specific heat at constant volumeCVis taken as a constant. This restriction results in a simple expression for internal energy in terms of temperature and specific volume. This expression contains an undefined function of volume which is shown to be calculable from the available experimental data. The resulting formulation agrees with existing data for condensed states of water to a high degree of accuracy in the region from 0.5 to 300 kbar.