Water and energy are two inseparable items that govern our lives and promote civilisation. The provision of fresh water is becoming ail increasingly important Issue in many areas in the world Absorption heat transformer systems are attractive to use solar energy, geothermal energy and waste heat from industrial process as heat source and delivering thermal energy to higher temperature than the temperature of the fluid by which they are fed In this paper a comparative study between single effect and double effect absorption heat transformer systems used for seawater desalination is carried out. The mathematical formulation will be based on mass, energy and exergy equations and conditions of thermodynamic equilibrium, considering lithium bromide-water as working mixture Simulation results were used to study and to compare the influence of the absorber temperature and the intermediate heat Source temperature (evaporator and generator temperatures) on the energy efficiency, exergy efficiency, and fresh water production of the two systems. The numerical results obtained will serve like a tool to predict the possibilities and limits of application of absorption heat transformers coupled to seawater desalination system (C) 2009 Elsevier B.V. All rights reserved