Photocatalytic hydrogen production in pure water for three component systems using a series of rhenium-based photosensitizers (PS) and cobalt-based water reduction catalysts (WRC), with triethanolamine (TEOA) as an irreversible electron donor, is described. Besides the feasibility of this reaction in water, key findings are reductive quenching of the excited state of the PS by TEOA (k(q) = 5-8 x 10(7) M-1 s(-1); Phi(cage) = 0.75) and subsequent transfer of an electron to the WRC (k(CoIII) = 1.1 x 10(9) M-1 s(-1)). Turnover numbers in rhenium (TONRe, H/Re) above 500 were obtained, whereas TONCo (H-2/Co) did not exceed 17. It is shown that the cobalt-based WRC limits long-term performance. Long-term performance critically depends on pH and the type of WRC used but is unaffected by the type of PS or the concentration of WRC. A quantum yield of 30% was obtained (H/photon).