Viscosity is resistance to flow. Viscous samples require special consideration. There are several separate issues, and these apply whether one desires to measure interfacial tension or contact angles. Viscosity is measured in milli Pascal seconds (mPa s) which is numerically identical to centi Poise (cp). Water has a nominal viscosity of 1cp or 1mPa s. Viscosity is a strong function of temperature, dropping rapidly as temperature rises. A good place to get reference values for viscosity is the CRC Handbook of Chemistry and Physics (www.crcpress.com).