Viscosity of Water
The viscosity of water measures its resistance to flow and is critical to its many functions. The low viscosity of water is important in its role as the solvent for life's chemical reactions and for blood circulation. The viscosity of water has been studied thoroughly because of the precision with which water flow must be controlled in many industrial applications.
Viscosity of liquids is expressed in a variety of units:
with the standard SI unit being the Pascal second or Poiseuille. That unit does not prove to be convenient for many uses, but note that the viscosity of water at 20°C is almost exactly 1 if expressed in centipoise or milli-Pascal seconds. So like its convenient density of 1 gm/cm3, water at 20°C provides a convenient comparison standard for viscosity.