Already ANswered ypour qstn. since U have asked twice,Re-answering=>
Water that is being electrolysed at high voltage or electrode potential which further dissociates into H2 and O2 gases.
Anode and Cathode two electrodes are being dipped into the water and the electricity is passed and nearly 1.23 volts are needed for the water dissociation. While during the peocess the Hydrogen is collected at Cathode and the Oxygen is collected at Anode side.