A large part of Li production comes from the exploitation of saline lakes and salars. Industrial processes for Li recovery from such resources have to deal with highly saline waters. It is therefore necessary to develop the knowledge of Li chemistry adapted to these contexts. The present work aims to present a new set of Pitzer interaction parameters able to describe the chemical behavior of the H-Li-Na-K-Ca-Mg-Cl-H2O system up to salt solubility, at 25 °C. In a previous work, the model was limited to the H-Li-Na-K-Cl-H2O system. It is extended here by including Ca and Mg, taking into account recently revised parameters allowing the thermal properties of the binary CaCl2-H2O and MgCl2-H2O systems to be represented. The consistent extension of the thermodynamic database was made possible by the study of the binary CaCl2-H2O system up to the supersaturated metastable region and of nine ternary systems, namely X-Ca-Cl, X-Mg-Cl and Ca-Mg-Cl (where X = H, Li, Na, K). The model was finally tested on five quaternary systems.