http://www.trifield.com/content/about-air-ions/means to measure if the gas is coming out ionized could be:
Make the gas pass thru a metalic pipe and measure the voltage of the pipe in relation to ground
Connect the pipe to ground and measure the current
If current is flowing on the high voltage source than this might mean that the gases are going out of water carrying charge....
I guess ground could be used too instead of the flow of air or another water cell,
The air or two isolated systems must be required for moving applications such as a car, since the car must be neutral to be safe
The cathode in the air arrangement could be a hot filament connected to ground... this way the thermal emission would allow for cascading effect if low pressure is used... Maybe not required....
The gases could pass thru two isolated tubes and than electricity could be re generated, i guess