The explicit version of the mean spherical approximation (MSA) is added to the SAFT-HR equation of state (EoS) to model aqueous alkali halide solutions. The proposed electrolyte equation of state (eEoS) has two parameters per each ion. Two methods are in common use for calculating ion parameters: ion-based and salt-based. In this work, the electrolyte parameters are obtained for 61 single electrolyte solutions using salt-based method. Using this approach, mean ionic activity coefficients of the 61 aqueous electrolyte systems were modeled with overall average absolute relative percent deviation (AAD%) of 3.91. Also, for testing the ability of the model in terms of ionic parameters, six salts (NaCl, NaBr, NaI, KCl, KBr and KI) were studied using ion-based method. The liquid densities, osmotic coefficients and salt mean ionic activity coefficients of 6 aqueous electrolyte solutions were modeled with overall AAD% of 0.68, 2.28 and 0.96, respectively.