Theoretical investigation of the rate constant and activation energy of the charge-transfer reaction in water is performed. Equations for these kinetic characteristics of the reaction obtained in the framework of quantum mechanical theory are presented. The equations take into account a quantum character of the O-O vibration and the fact that the dielectric spectrum.of^water has an absorption in the quantum frequency range. Parameters of these equations, such as the reactants' interaction free energy in water, U(R), electron coupling matrix element, Vfi, and reorganization energies are calculated in terms of appropriate models for several mutual geometries of the reactants. For each of these geometries, the distance dependence of the parameters is investigated and used for numerical estimation of the rate constant and activation energy. Results of the theoretical analysis are in a reasonable agreement with experimental data.