The water absorption behavior has been studied for poly(ethylene oxide) films (PEO) and for films of M(CF3SO3)2PEOn with M = Zn and Pb and n in the range of 9 to 24. Quantitative measurements of the kinetics of water absorption have been made. Proton nuclear magnetic resonance (NMR) spectroscopy has been used to characterize the effects of water absorption on the polymer properties, such as degree of crystallinity and polymer chain mobility. Impedance spectroscopy measurements have also been performed on humid samples. Water absorption is found to increase the mobility of the polymer chain as well as the ionic conductivity of the electrolyte, and a possible mechanism for these effects is proposed. Water absorption also causes a decrease of the amount of crystalline phase present in the sample. In addition, deuteron NMR has been used to study the mobility of the absorbed water, demonstrating the absence of liquid water surface layers on the polymer, and that the conductivity increase observed upon hydration is a property of the hydrated polymer electrolyte itself.