Water diffusion in four hard-soft block copolymer systems, based on poly (butylene terephthalate) as the hard segment and a copolymer with poly(ethyleneoxide) (PEO) as the soft block, has been investigated by pulsed field gradient echo NMR. The water absorption and the water diffusion coefficient depend on the composition of the copolymer and the amount of water absorbed in the system. The higher the fraction PEO in the polymer the higher the amount of absorbed water and the faster the water diffusion. The diffusion experimental results further indicate an interaction between water molecules and the PEO units in the soft segments. For all investigated systems it is found that water molecules reside near PEO units within a distance of less than 0.5 nm for a time of the order of or longer than 1 ns. The higher the amount of PEO in the soft blocks, the shorter the residence time of the water molecules near the PEO units.