To observe if it is possible to improve agreement to thermodynamic parameters over the OPC or the Force Balance family of models, we fit water model parameters directly to experimental G res (T, P ) and all of the response functions of G res (T, P ). We do not restrict our model to any particular geometry, and instead perform a multidimensional optimization in all six variables and fit to multiple thermodynamic property surfaces over a range of temperatures and pressures, simultaneously. The methods section shows the development of this powerful new force field parameterization scheme. So far, water models have been fit to property isobars, i.e. property curves estimated at 1 atm and several temperatures. Thus, the current water models may have reduced the errors in properties that come from the temperature derivative of Gibbs energy to the maximum extent. However, errors in the properties estimated using the pressure derivatives of the Gibbs energy remain unaddressed, especially at pressures higher than 1 atm. While fitting the water model to experimental property surfaces, we therefore put more emphasis, by using suitable weights and constraints, on the properties estimated using the pressure derivatives, particular molar volume, while keeping the errors in the temperature derivative properties like enthalpy and heat capacity levels at or below those of other accurate water models.