Polarized Raman spectra of betaine potassium bromide dihydrate were studied in the broad spectral range 5-3600 cm^-1 and in the wide temperature interval 30-292 K, with special emphasis on the structural phase transition at 160 K, recently discovered. It is shown that this phase transition is related to the freezing of the successive reorientations of the water molecules. Peculiar features and the temperature evolution of hydrogen bonding in this compound are discussed.