Hydration of borosilicate glass (Coming Pyrex glass) in isotopic water (H2O)-O-18 vapor was performed at different temperatures. The depth distributions of H-1 and O-18 in the borosilicate glass measured by the Time-of-Flight Secondary Ion Mass-Spectrometry (TOF-SIMS) were found to be drastically different. The activation energies for the O-18 diffusion and for the glass hydrogenation were measured experimentally. The depth distribution of the O-18 isotope was described well by the complementary error function, whereas the depth distribution of hydrogen represented the so-called "S-curve". A similar hydrogen distribution was observed earlier in hydrated natural aluminosilicate glasses (obsidians). This led us to the conclusion that the hydrogenated layer was formed due to a solid state chemical reaction between protons and the glass network. The protons were the result of another solid state chemical reaction between the absorbed water molecules and glass network occurring in a top surface layer (< 30 nm).