A process and apparatus for water purification has a stationary electrode opposing a movable electrode which are positioned about a passageway for the water to be purified. The stationary electrode and movable electrode form an arc gap, and the arc gap is fed with a voltage from a pulsatile power supply. The arc gap is reduced when the current is below a first threshold and increased when the current is above a second threshold, and the arc gap change is realized by controlling a motor attached to feeder rollers coupled to the movable electrode. The apparatus causes the formation of oxide nano-particles providing durable bactericidal action.