An investigation was carried out of the molecular interactions and local relaxation dynamics in glassy polymer networks exposed to moisture. Stoichiometric and off-stoichiometric mixtures of the diglycidyl ether of bisphenol A (DGEBA) and diethylene triamine (DETA) were prepared, cured, and investigated. The, physical and the chemical nature of the interactions between the network and the absorbed moisture were studied by broadband dielectric relaxation spectroscopy (DRS), Fourier transform near-infrared (FT-NIR) spectroscopy, and molecular simulations. Dry networks are characterized by two Arrhenius-like local relaxations: the beta process, associated with hydroxyl groups, and the gamma process, associated with primary and secondary amine, and glycidyl ether groups. Absorbed water interacts with the network and affects the dynamics of beta and gamma processes. FT-NIR spectra reveal the presence of three forms of water molecules, differing in the number of hydrogen atoms (0, 1, or 2) that participate in hydrogen bonds. The relative ratio of each form to the total absorbed water was calculated from the NIR data and from molecular simulations. An excellent agreement between those two techniques was observed.