Tris(2,2′-bipyridyl)ruthenium(II) photosensitised electron transfer from EDTA to methyl viologen in aqueous solution and the reduced form of the viologen was used to reduce water to H2. The rate of formation of H2 was dependent upon the light intensity, the pH of the solution, the type and concentration of catalyst used for the water reduction step and the concentrations of chromophore, EDTA and methyl viologen. These factors were optimised for H2 production and alternative types of viologen were tried but none was superior to methyl viologen. The significance of these findings towards the cyclic cleavage of water into H2 and O2 is described briefly.