no wires needed the outer plate contacts water there's direct conduction... simple stainless steel should work...if the metal oxidizes there's no conduction after... only on the inside of ccapacitor a dielectric layer is needed to insulate, it would be goood if once the capacitor is formed there's a discharge with a spark to the outer plate.. if the gap is adjusted to breakdown only when voltage is increased , regular dielectrics when they breakdown they are done, maybe some dielectric that is immune to this effect like some oxides?