This study concerns the properties of the concentrated bittern solutions occurring as by-product from solar salt works, in relation to their potential use as liquid desiccants in cooling systems. Solutions of compositions similar to those of bitterns have been made up in the laboratory, as have concentrated mixtures of MgCl2-MgSO4-H2O. Measurements of vapour pressure have been carried out using an isoteniscope and are reported together with measurements of density and viscosity. Several theoretical models representing these properties are reviewed and compared against the experimental results; the average agreement between theory and experiment is within 5% for vapour pressure and better for the preferred models of the other two properties. Based on these findings, an expression is provided for the equilibrium relative humidity of bitterns as a function of concentration relative to raw seawater. The vapour pressures of bittern solutions are found to be similar to those of solutions containing only magnesium chloride but having the same mass fraction of total salts. Therefore magnesium chloride solution is a reasonable model for bitterns for the purpose of developing the proposed cooling system. (C) 2009 Elsevier B.V. All rights reserved.