In this study the suitability of brackish groundwater quality for reverse osmosis (RO) desalination is evaluated. The results of initial laboratory and field analysis of 41 production wells were used to determine the hydrochemical properties of groundwater for both the Dammam limestone aquifer and the clastic Kuwait Group aquifer in the southwestern part of the State of Kuwait. The core samples of these wells were collected and analyzed in order to determine the hydrogeological properties of the same aquifers in the Umm Gudair area. Hydrochemical data of these aquifers were analyzed to help describe relations between hydrochemically distinct bodies of water and elucidate links between hydrochemical data and hydrogeological parameters. During this study, the Expanded Durov diagram was simplified and linked with the Sulin classification method in order to give more interpretation values. The results show that the aquifer materials influence the quality of ground water in each aquifer. The Kuwait Group aquifer water is characterized by Cl-Mg and Cl-Ca genetic water types with an average TDS of 4008 mg/l and belongs to the chloride water type. The Dammam limestone aquifer water characterized by the Na-SO4 and Cl-Mg genetic type with an average TDS of 3480 mg/l belongs to the sulphate type. Both aquifers contain suitable water for RO desalination since they have a high concentration of chloride and monovalent ions, which reduces the requirements of antiscalant additives.