This thesis forms a record of the investigation carried out by the author on the correlation of the thermodynamic properties of ordinary water substance. The background to this problem was thoroughly explored and is discussed together with details of the latest international developments. Attention is drawn to the fact that the derivation of so-called 'Thermodynamic Temperatures' by the addition of the quantity, 273.15, to temperatures referred to the International Practical Temperature Scale leads to discrepancies in the values of the thermodynamic properties calculated from equations of state by means of the thermodynamic relations. These differences are shown to be significant when compared with the tolerances in the 1963 International Skeleton Tables. Equations in the form of Chebyshev polynomials are presented which enable the thermodynamic properties of saturated water and steam to be calculated in a systematic manner. In the equation defining the pressure-temperature relationship allowance has been made for certain unpublished measurements of the National Bureau of Standards. Accurate tables of saturation properties for regular intervals of temperature are included. A new equation for compressed water from 1 to 1000 bar and 0 to 15
