[thedoc (OP)]

Michael Wadsley asked the Naked Scientists:
   G'day
How does one differentiate between electrical polarisation and charge separation in a liquid dielectric material such as water?  Most descriptions of the bending of a stream of liquid water in an electric field take it to be evidence for the polarisation of the water molecules.  However I believe that the Kelvin water dropper (and other published evidence) demonstrates macroscopic charge separation in water in an electric field because the falling water drops acquire positive or negative charges when they separate from the continuous water feed.  I would accept the possibility of both polarisation and charge separation occuring simultaneously but I believe charge separation cannot be ignored and should be included in explanations of bending a water stream.
Michael
PS I enjoy your session on Radio National
What do you think?

[chiralSPO]

The conductivity of normal tap water is typically quite low (very small concentration of dissolved ions). These ions will certainly move under the influence of an electric field, and are certainly a contributing factor. The main question is how significant is this? It might be worth doing an experiment using aqueous solutions of different ionic strengths, and quantifying the deflection of the stream as a function of ionic strength. It is also possible to use highly purified water (I have some 18.2 MΩ water in the lab I might just play around with), for which ionic species should be negligible. It could be interesting to look at the behavior of non-aqueous polar liquids, but I think differences in density, surface tension and viscosity would probably dominate over dielectric strength and polarity/polarizability...