With reference to mechanisms of formation of the electrolytic plasma, I found this paper: Electrolytic plasma technology: Science and engineering - An overview
According to classical interpretation, plasma is formed into little bubbles that are formed in the process and that have a quite high electric field accross them (e.g. 30V accross a 10um boubble imply an enectric field of 3000 V/mm, that is close to the breakdown voltage for some gases).
If this theory is true, it should be possible to get electrolytic plasma by applying a relatively low voltage to deionised water (less than 50V, but dependent on the cell geometry) and then by adding some sparkling water!
Two things may happen: a) no plasma is formed: this imply the classical theory is not correct; b) plasma is formed in small boubbles far from electrodes: this gives interesting opportunity to study the behaviour of these entities, without the interference of cathodic reactions.