This paper describes a procedure to precisely decouple the electrostatic and the nonelectrostatic contributions to the water activity of an electrolyte solution, using the partial molal enthalpy of water in the electrolyte solution. This work is an extension of our previous work [Sahu et al. in Fluid Phase Equil. 460:57–68, 2018, Data in Brief 19:485–494, 2018], where a methodology to segregate the electrostatic and non-electrostatic contributions to the water activity was discussed and the constancy of the electrostatic contribution to the water activity was shown. However, in this paper, it is a noticeable point that even a 2% variation in the electrostatic contribution to the water activity leads to a very large deviation in the electrostatic contributions to the partial molal enthalpy of water. Therefore, due to the high sensitivity of the enthalpy to the variation of the water activity, the partial molal enthalpy of water is used for refinement of the method of partitioning the water activity into electrostatic and nonelectrostatic contributions and to provide the physical interpretation of the electrostatic and nonelectrostatic contribution to the partial molal enthalpy of water. This paper also describes the procedure to estimate the partial molal enthalpy of water from the water activity of the electrolyte solution. Microcalorimetr has been used to estimate the closed spaced points of partial molal enthalpies.