When glass particles adsorb water from humid environments their low frequency dielectric properties change drastically. To investigate the polarization mechanism, variable frequency measurements upon individual glass particles (similar to 50 mu m diameter) suspended in silicone oil were performed with a computer-controlled dielectrophoretic levitator. The electrical properties of individual particles have been measured in the frequency range between 10 Hz and 100 kHz. A relaxation in the induced dipole moment of moistened glass particles suspended in silicone oil is clearly evident in measured spectra. Surface moisture causes the characteristic relaxation times of soda-lime glass particles to change by up to 5 orders of magnitude. The relaxation spectra are satisfactorily modeled by the Debye equation and a model based on ohmic surface conduction appears to explain the phenomenon. This research has potential implications with respect to the controversy surrounding the influence of moisture on the performance of electrorheological fluids.