It is shown on the basis of the data of three complementary methods (NMR-relaxation, Car-Parrinello molecular dynamics and quantum-chemical calculations) that the environment of the cation Ca2 + in aqueous solutions consists of two layers with different molecular mobility: the number of water molecules in the first hydration shell is n1 = 6, and for the second hydration shell n2 = 12. The obtained n1 and n2 values were slightly rounded up to the nearest integer values to make the model more clear-cut (it is significant that the required changes were considerably < 5%).