We have performed experiments to determine the density of water at pressures and temperatures of 9.5 to 25 kbar and 930 to 1600°C, respectively. The experimental method involved growing inclusions of fluid (ρ < 1.0 gm/cm3) in synthetic precracked corundum. Density was determined by measuring the homogenization temperature along the liquid-vapour equilibrium curve. Comparison with the many current equations of state for water indicates that, in the P-V-T range of the experiments, the equations of Kerrick and Jacobs (1981) and Brodholt and Wood (1993) provide the best fits. In contrast the steam tables of Haar et al. (1984) systematically underestimate the molar volumes at high temperatures.