The rotational dynamics in liquid water have been studied. The power spectra of the single-molecule orientational autocorrelation function (ACF) have been calculated in molecular dynamics simulations with the SPC/E potential and have been used to characterize various rotational motions of water molecules. Both ordinary and heavy water have been examined at temperatures of – 10 and 25 °C. For liquid H₂O at 25 °C the power spectra of the second-order (Raman) orientational ACFs contain three intense bands, centred at ca. 500, ca. 560 and ca. 670 cm^–1, and a less intense high-frequency shoulder at ca. 820 cm^–1. Two intense librational bands with maxima at ca. 570 and ca. 650 cm^–1 are present in the power spectrum of the single-dipole orientational ACF for the same system. The average temperature coefficient for the librational frequencies of SPC/E water is found to be about –0.65 cm^–1 K^–1, which agrees well with experimental estimates. A well resolved rototranslational band centred at ca. 55 cm^–1 is observed in the low-frequency region of the power spectra of the single-molecule orientational ACFs. This band is relatively insensitive to temperature variations and shows no isotopic effect.