The type of water used is not important, just as Stan said. When the water is polarized it can be charged.
This is because the chokes are used to restrict the amps, not block them entirely as some leakage is necessary to start the process. Then as gas forms, the capacitance will start to decrease. Start at lower voltage, like 2V. Otherwise you won't have room to gradually increase the voltage and retune resonance as the capacitance decreases. This allows you to gradually maximize the charge.