Desalinated brackish water is becoming an important water source for agricultural irrigation, a fact which raises the incentive to include a minimal Mg2+ concentration in the product water, which would minimize fertilization requirements. Both the mineral content and chemical stability of desalinated water are attained through the post treatment stage at the desalination plant. A modified post treatment process is introduced, in which Mg2+ ions are separated from the brackish water fed to the desalination plant via a selective cation exchange resin, and subsequently released to the product water through further exchange with Ca2+ ions previously generated in a common H2SO4-based calcite dissolution process. Calcite dissolution provides the water with carbonate alkalinity, Ca2+ and SO42-, while the ion exchange step adds Mg2+. Laboratory and theoretical investigations of the process show that it results in a high water quality, attained in a cost effective and environmentally friendly manner. Three case studies are presented in which the additional cost of supplying Mg2+ concentration of either 12 or 18 mg L-1 using the process is estimated at less than $0.006 m(-3) product water. The results indicate that the process is feasible for brackish waters characterized by Mg2+ to Ca2+ concentration ratio higher than 1:1. (C) 2010 Elsevier B.V. All rights reserved.