what is the mechanism of water conductivity?

I'm trying to wrap my head around the kelvin water drop generator and more specifically what happens in the water before it drops. If on one side the drops of water are positive and on the other side negative, that means there is current flowing through the water before it drops.

What I dont understand even more specifically is how electricity is carried by water, and why water conductivity increases with ions content (and other impurities perhaps).

Are there electrons flowing ? Or are there ions flowing ? Let's imagine that we are below the potentials at whitch electrolysis occurs (about 1 volt). What carries the charges ?

I first thought that ions were responsible for the charges in the kelvin generator, but when a spark occurs, because the water has dropped into separate boxes it's impossible for them to move, so there must be some kind of redox reaction occuring. But if table salt is in the water to raise it's conductivity, would that mean that Na+ is reduced to sodium and Cl- oxydized to chlorine ?

• Water is an insulator. When you add salts, sat $\text{NaCl}$, you get ions and make water a conductor. – jinawee Jan 8 '14 at 20:09
• reading several other similar questions on stack exchange it seems this is considered a chemistry question, the most in depth answer on chemistry SE I found so far is : chemistry.stackexchange.com/questions/4979/… – Manu de Hanoi Jan 9 '14 at 6:31