Rapid water oxidation catalysis is observed following electrochemical oxidation of [Ru-11(tpy)(bpz)(OH)](+) to [Ru-V(tpy)(bpz)(O)](3+) in basic solutions with added buffers. Under these conditions, water oxidation is dominated by base-assisted Atom Proton Transfer (APT) and direct reaction with OH-. More importantly, we report here that the Ru-IV=O2+ form of the catalyst, produced by le(-) oxidation of [Ru-11(tpy)(bpz)(OH2)](2+) to Ru(III) followed by disproportionation to [Ru-IV(tpy)(bpz)(O)](2+) and [Ru-IV(tpy)(bpz)(OH2)](2+), is also a competent water oxidation catalyst. The rate of water oxidation by [Ru-IV(tpy)(bpz)(O)](2+) is greatly accelerated with added PO43- with a turnover frequency of 5.4 s(-1) reached at pH 11.6 with 1 M PO43- at an overpotential of only 180 mV.