We are proposing 10 days of beamtime on IRIS to investigate the diffusion process of H2O molecules adsorbed on polyamide, surface material of reverse osmotic membranes currently used for desalination and waste-water reclamation. Their ability for HBO3 removal is believed to depend on the diffusivity of water near the membrane. Four samples will be measured using partial deuteration to separate the dynamical contributions; polyamide (C30H7D13O7N6)n with x% of H2O and polyamide (C30H13D7O7N6)n with x% of D2O (x = 7 and 15). From these data, we can discuss the motional coupling between water and polyamide network as well as the diffusive motion of water. This work will play an important role in revealing the mechanism controlling the ability of HBO3 removal by these reverse osmotic membranes.