Arcing during water bridge, which dielectric breaks down first?

[HelloCthulhu]

I've been interested in the effects of electric fields on water for a while and came across this impressive demonstration of the water bridge experiment:



The thing that fascinates me the most is how much the electricity arcs out of the water. For example at timestamp 8:43 the arc clearly goes across both beakers until more water is added. I know that water is being ionized, but does it reach its dielectric breakdown before or after air? Intuitively water breaking down first is the only thing that makes sense since it's actually touching the electrodes, but I don't know enough about dielectrics to be sure.

 

[trurle]

I've been interested in the effects of electric fields on water for a while and came across this impressive demonstration of the water bridge experiment:



The thing that fascinates me the most is how much the electricity arcs out of the water. For example at timestamp 8:43 the arc clearly goes across both beakers until more water is added. I know that water is being ionized, but does it reach its dielectric breakdown before or after air? Intuitively water breaking down first is the only thing that makes sense since it's actually touching the electrodes, but I don't know enough about dielectrics to be sure.

Water is actually very tricky dielectric. Its dielectric strength is time-dependent. If voltage applied for longer time, the dielectric breakdown become easier. But in general, deionized water break after the air.