Information on the state of proton and water molecules in sulfostyrene ion exchangers was obtained by joint application of thermodynamic and quantum chemistry methods to experimental water sorption isotherms from paper B.R. Sundheim, M.H. Waxman, H.P. Gregor, J. Phys. Chem., 57: 9 (1953) 974-978. The model of Predominant Hydrates in combination with non-empirical quantum chemical calculation was used for calculation of theoretical water sorption isotherms. The experimental water sorption isotherms can be accurately described by the model accounting for the presence in the resins with different cross-linkages (0.4-23% DVB) of four hydrates (H3O+; H3O+center dot H2O; H3O+center dot 2H(2)O; H3O+center dot 6H(2)O) with practically the same Gibbs energy formation (stability constants). The IR and Raman spectra of dry and hydrated resins were interpreted by comparing theoretically calculated spectra of p-ethylbenzene sulfonic acid and experimental ones. Some corrections to their interpretation were suggested. The spectra show that complete dissociation of sulfonic groups occurs after sorption by the resin three water molecules per sulfonic group. (C) 2016 Elsevier B.V. All rights reserved.