Liquid light and heavy water are the most widely used moderator and reflector materials in nuclear reactors, however there is a lack of knowledge of the vibrational density of states of as a function of temperature that match the quality of data achievable with the present-day neutron facilities. The Nuclear Engineering reactor calculations make resource of old spectra, and their temperature variation is ill-known. The quality of the present day calculations make imperative an update in the knowledge of the spectra. Being MARI the best spectrometer to study densities os states, we propose to measure two samples of water in liquid phase (heavy and light) at three temperatures each (300 K, 350 K and 395 K). The data will be processed on the basis of our previous knowledge by multiple scattering and attenuation, and also multiphonon effects.