The results of a combined study of dielectric loss (epsilon' '(nu)) and power-absorption coefficient (alpha(nu)) are reported. The epsilon' '(nu) and alpha(nu) values are obtained for liquid water (H2O) and heavy water (D2O) using analytical modeling and the molecular dynamics (MD) simulations method. The calculated spectra span the microwave and far-infrared (FIR) region. The temperature range probed is 220-355 K. Appropriate parametrization of the analytical model for liquid water enables the quantitative description of the dielectric spectra over the frequency range of 0-1000 cm(-1). An excellent agreement between the calculated spectra and the experimental data demonstrates the accuracy of the applied analytical approximations. The spectra obtained using the MD simulations agree rather qualitatively with the experimental epsilon' '(nu) and alpha(nu) dependences. The observed spectra are interpreted in terms of four molecular mechanisms that have been recently described [J. Phys. Chem. A 2006, 110, 9361].