The infrared spectrum of water, isolated in inert matrices, has been studied in the interval from 60 to 4000 cm(-1). Experiments with partially deuterated water combined with DFT (density functional theory) calculations have been used to investigate the structure of matrix-isolated water tetramer. A few, strong intermolecular fundamentals of the water tetramer have been observed. Mid-infrared bands due to deuterated pentamers and hexamers have been observed and are used to discuss the assignments of these water clusters.