Converging UV-vis, EPR, rRaman, and DFT calculations highlight the evolution of [Ru-4(H2O)(4)(mu-O)(4)(mu-OH)(2)(gamma-SiW10O36)(2)](10-), 1, to high-valent intermediates. In analogy with the natural enzyme, five different oxidation states, generated from 1, have been found to power the catalytic cycle for water oxidation. A high electrophilic tetra ruthenium (V)-hydroxo species is envisaged as the competent intermediate, undergoing nucleophilic attack by an external water molecule as a key step in the formation of a new O-O bond under catalytic conditions.