The ideal gas equation of state is thesimplest equation of state for estimating the values of temperature, pressureand volume. This equation of state has a simple structure based on its simpletheory. Hence, it has an explicit relation between these variables. In addition, calculating otherthermodynamic properties (such as, internal energy, enthalpy and specificheats) is very simple for ideal gases. In this study, the ideal gas theory hasbeen applicable for the liquid and vapor phases of water. To this aim, thetemperature and molar volume have been modified as functions of the fluidmolecular compressibility. In the presented method, effects of the temperatureand volume on the non-ideality of the behaviors are considered, separately. Comparingthe predicted values with the real data shows at least R-squared value equal to0.98.