We present in this work a systematic study to analyze the influence of water and filler content on the dielectric response of silica-filled rubber compounds. For nanoparticle-filled polymers an additional dielectric process is usually observed in the loss dielectric spectra at frequencies lower than the alpha (alpha) or segmental relaxation. This process has generated some controversy in the literature due to the different (sometimes contradictory) interpretations given to explain its physical origin. We demonstrate, by means of dielectric spectroscopy in combination with thermal analysis, that this low-frequency process is compatible with a MWS process enhanced by the presence of water molecules at the silica surface. We show that the frequency of the maximum for this process is strongly affected by the amount of water attached to the silica particles. The dielectric response of the MWS process is rationalized by means of a simple interlayer model (IL). In addition, we also study the influence of water and filler content on the segmental dynamics and discuss possible mechanisms for the filler-polymer interaction.