Traces of moisture adsorbed in nanoporous silica films were measured in nanograms using a quartz crystal microbalance. Even small concentrations of surface modifier used to treat xerogel greatly reduce the moisture in the films. Moisture adsorption is greater for films of higher porosities, most likely because of the increased surface area. By employing two different surface modifiers, it was demonstrated that the level of hydrophobicity is a function of surface chemistry, and thus can be tailored by using a suitable surface modifier. (C) 2002 The Electrochemical Society.