Experimental studies on the plasma initiated in ultrapure water between pairs of tungsten and lanthanum hexaboride electrodes have been performed. The current - voltage characteristics showed the features of a spark discharge for the both types of electrodes used in the process. The breakdown voltage depended on the work function and on the surface morphology of the electrodes. The reactive species formed in the water plasma and their emission intensity depended on the electrode material. (C) 2011 Elsevier B. V. All rights reserved.