A model for a sustainable desalination process has been developed. The simulated process consists of pumping seawater through a solar heater before flashing it under a passively created vacuum in an elevated chamber. The vacuum enhances evaporation and is maintained by the balance between the hydrostatic pressure inside the elevated flash chamber and the atmospheric pressure. The developed model uses theoretical thermodynamic relations to describe the process setting it apart from previous empirical correlations. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 1196-1203, 2010