Statistical Associating Fluid Theory coupled with Restricted Primitive Model (SAFT1-RPM) represents the mean ionic activity coefficient, density, osmotic coefficient, and va-por pressure of several aqueous alkali halide solutions, in a framework that is analogous to the non-electrolyte framework. SAFT1 alone represents pure water, including the den-sity anomaly. Each SAFT1 salt molecule consists of two segments: cation and anion.