Many researchers have reported an improvement of the properties of polymer dielectrics by introducing nanofillers. However, the influence of ambient conditions and sample storage under different conditions are often not taken into account. The epoxy matrix itself is a polar polymer susceptible to water absorption, and the presence of hydrophilic nanofillers such as silica will enhance the uptake of moisture from the environment. The dielectric response both of neat epoxy resin and an epoxy-based nanocomposite under an electrical stress greatly depends on the amount of absorbed water. This study investigates the effect of water absorbance on the dielectric spectrum of epoxy-silica nanocomposites containing different concentrations of nanoparticles.