Thermodynamic calculations of solubility diagrams were carried out for four-component systems with a common ion and four-component reciprocal water-salt systems containing sodium and potassium chlorides, sulfates, carbonates, and hydrocarbonates at temperatures from -5°C to + 35°C. Pitzer's equations were used to approximate the variations of excess thermodynamic functions with solution composition. The calculation results are well consistent with experimental solubility data and can be used to simulate salt crystallization in the evaporative basins with the carbonate type of water.