Using an intracavity spectrometer with a neodymium glass laser with a spectral resolution of 0.035 cm−1 and threshold absorption sensitivity of 10−8 cm−1, water vapor absorption spectra have been studied. The H2O and HDO absorption spectra have been recorded in the temperature interval of 300–1000 K. The spectra have been identified, and many new energy levels of the H2O and HDO molecules have been determined. Coefficients of line center shifts induced by pressures of H2, O2, Ar, Xe, and Kr buffer gases and of the atmospheric air have been measured. For all buffer gases, a linear dependence of the shift magnitude on the pressure was observed. For a proper measurement of the coefficients of the line center shift, a technique employing a temperature-stabilized Fabry-Perot interferometer has been proposed.