Leaders are characterized by a very low internal electrical resistance, which results in a negligible voltage drop, thus the voltage gradient across the plasma–liquid interface is independent of the position within the plasma area. This uniform voltage gradient coupled with the uniform conductivity of the water produces a uniform current density, which means that the discharge current is directly proportional to the area of the plasma–liquid interface. It is clear from Fig. 6 that the relationship between the peak discharge current (Imax,meas) and plasma area is not perfectly linear. This non-linearity is because a higher discharge current corresponds to a higher discharge rate and therefore a higher rate of reduction in the discharge voltage. Consequently, the discharge voltage at the time that corresponds to Imax,meas decreases with increasing plate size, causing the Imax,meas vs. plasma area curve to level off for larger plate sizes. The effect of this varying voltage was accounted for by comparing Imax,meas to the theoretical maximum current (Imax,thry) calculated from Ohm’s law (Table 2):