To reduce the number of adjustable parameters that appear in the thermodynamic modeling of hydrogen-bonding fluids, the use of ab-initio molecular orbital calculations in the form of Hartree-Fock and density functional theories to compute thermodynamic properties are considered. In particular, the enthalpy and entropy changes on hydrogen bonding for water are computed. The theory the computational methods and the basis sets used, as well as the results far water, are discussed The results obtained are compared with those of others and with experimental estimates from the literature to determine the validity of the methods that are then used in this extended study The results obtained here are also used to examine the validity of mixture group contribution methods for hydrogen-bonding mixtures, to develop simple estimation procedures for model parameters and to reduce the number of calculations arch as those described that need to be done.