no plain water is involved but since the reaction is taking place in water SOLUTION the water is what is being evaporated therefore creating hydrogen (gas). Depending on the control variables you have (temp, pH, etc.), your reaction could either produce CI2, CIO-, or O2. Since it has such a high calcium concentration... it is probable that the Ca(OH)2 or whichever similar chemical used would then break out and cover the cathode, therefore resulting in H2 generating an electrode.
hope it helped:)
