Understanding water-membrane interactions is a fundamental issue in biophysics since these interactions are at the basis of many key molecular processes occurring in membranes. The hydrogen-bond network of water molecules is highly dynamic and its dynamical structure influences membrane fluidity and proton transport across membranes. We investigate the dynamics of water hydrogen-bonds network in model membranes using dielectric relaxation spectroscopy in the TeraHertz range. This frequency interval is suitable for obtaining information on the collective low-energy modes of the hydrogen-bond network of water molecules. In this paper we review the technique and present some preliminary experimental results.