Paper published Jan 16, 2016
link to journal; full text (PDF)
Water flowing through tubes of different materials and collected in a Faraday cup contains net electric charge. Water charge is always positive but its magnitude depends on the material position in most triboelectric series. On the other hand, water acquires net negative electric charge when falling through air but its charge is modified after it passes through an electric field. Thus, water is located on the top of the triboelectric series and its charge is a robust and reliable way to organize materials within the triboelectric series, giving due attention to its surface properties.