A new equation-of-state model is presented that accounts for the nonrandom distribution of the free volume, as well as of the molecular segments, in systems of fluids interacting with strong specific forces. Expressions for the basic thermodynamic quantities are derived for pure fluids and for mixtures. The new formalism is applied to the description of the volumetric behavior of water at near-critical and supercritical conditions. The vapor pressures of subcritical water are also calculated. The degree of hydrogen bonding at these conditions is estimated and compared with the results of NPT molecular dynamics calculations and with available experimental data.