What happens if water is treated to AC power supply of 12 kV and 14 kHz?
Using up to 30 kilovolts is not uncommon with aqueous systems in a technique called capillary electrophoresis. Similarly, applying kilohertz current is also common in a technique called conductometry to measure the resistance of aqueous solutions.
In general, when you pass high frequency current, electrolysis does not occur.

You have to check the dielectric breakdown voltage of water, perhaps with high voltage and high frequency current, severe Joule heating would be observed, if there is no dielectric breakdown (which means internal sparking).