Halogen-substituted perovskites Ba_4In_2Zr_2O_10.95F_0.1 and Ba_4In_2Zr_2O_10.95Cl_0.1 are synthesized, and their single-phase composition is verified by X-ray diffraction analysis. Their ability of the studied phases to hydrate and form energetically unequal OH^– groups is proved. It is found that introduction of halide ions leads to a decrease in the hydration degree with respect to the matrix composition, which is explained by a decrease in the crystal unit cell free volume Processes.