A new thermodynamic model has been developed for molten salt-water solutions. The model applies particularly to salt-rich solutions but may be applied over the entire composition range from anhydrous salts to pure H2O. The model is an extension of the two-sublattice Modified Quasichemical Model for molten anhydrous salt solutions with first-nearest-neighbour short-range ordering. The model assumes the existence of hydrated cations such as K(H2O)(j)(+) and Ca(NO3)(k)(2+) as well as "free" neutral H2O molecules. The model has been used in a complete critical evaluation and thermodynamic optimization of the three binary systems KNO3-Ca(NO3)(2), KNO3-H2O and Ca(NO3)(2)-H2O and of the ternary system Ca(NO3)(2)-KNO3-H2O. (C) 2018 Elsevier Ltd.