Research on the thermodynamics of electrolytes is timeless, and modeling an electrolyte solution might be considered to be a golden oldie, which was, is, and will be important in the design of processes and new materials in the future. The reason is that electrolytes play important roles in different scientific disciplines, such as material development, technical processes (chemical industry, biotechnology, and pharma and food industries), and most recently the energy sector. Closely connected is the further development of advanced thermodynamic models. The age of digitalization requires robust physical models as the basis for static and dynamic process modeling, and that will provide the basis for surrogate approaches in future machine learning developments. This all brings thermodynamic modeling to a consideration of its most important feature. There are many thermodynamic approaches which have been developed to correlate, model, and predict the properties and phase behavior of electrolytes. Usually, this has been very successful for aqueous electrolyte solutions. However, for solutions with poor water content, electrolyte modeling is challenging. This mini-review summarizes the recent advance of thermodynamic models for electrolyte solutions in a water-poor medium and suggests the required theoretical framework.