Water oxidation by Ti(OH)4 in the ground and excited states was investigated using density functional (∆SCF, TDDFT) methods gauged by the coupled cluster (CCSD, CCSD(T)) calculations. O2 and H2 are generated in a reaction sequence that starts with Ti(OH)4 reacting with H2O. This reaction can proceed by either nucleophilic attack by H2O or by H-atom abstraction from H2O. The nucleophilic attack has high energy barriers (40-120 kcal/mol) in both the ground and excited states. On the other hand H abstraction is effected by Ti(OH)4 in the excited state with a low energy barrier (4-8 kcal/mol), generating OH*. This is the rate-limiting barrier in the chain of O2 formation reactions proposed in this work. The production of free OH* radicals is not energetically feasible in the ground state. By absorbing two photons, two hydroxyl radicals are produced, which then form H2O2: By a stepwise H-abstraction from H2O2 and OOH*; O2 is generated by absorbing two more photons. In each H-abstraction reaction a Ti(OH)4 is consumed and a Ti(OH)3H2O is produced. H2 production can proceed thermally from the latter in a very exothermic (68- 105 kcal/mol) bimolecular reaction. The solvent effects, modelled by explicit water molecules, have a limited influence on the reactivity.