Simple BrainTeaser: Running an AC current between two independent amplifiers
Current flows in complete loops.

Charge is the time integral of current. If a current was flowing, the charge of one device would be increasing and the other would be decreasing, creating an electric field to oppose that current.



You can try using the capacitance to ground/self capacitance as the return path but beware a tank of water has a much higher self capacitance than your device can, so very little of the current will flow through the other device.



This is similar to how capacitive touchscreens work.