In this study, a systematic analytical methodology is described to establish a phase diagram based on the application of the model of regular solutions for ternary aqueous inorganic-organic and organic-organic systems. For this purpose, saturated aqueous solution of a single solute is characterized. Critical a(w) and solubility are measured using different methods. Critical analysis and comparison with literature data allow selecting the best method for our systems to use the values and apply the regular solutions model to binary solutions and then to ternary ones. Thanks to solubility, water activity and alpha-parameter determination,it is shown that it is possible to apply the regular solutions model to experimental points of water activity and to obtain a very good agreement between the model and experimental data. The advantage of applying the regular solutions model is to predict water activity of mixtures by evidencing interactions in ternary mixtures. The final aim is to predict stability range of crystalline mixture according to storage conditions. (C) 2017 Elsevier Ltd. All rights reserved.