A Cu(ii) coordination polymer, [Cu(tza)2]n (Htza, tetrazole-1-acetic acid), was investigated as an efficient water oxidation catalyst in the well-established Ru(bpy)32+/S2O82- (bpy = 2,2'-bipyridine) photocatalytic system. The turnover frequency (TOF) was measured to be 1.68 s-1, which is the highest among all reported copper-based photocatalytic water oxidation systems.