RuO2(110) exposes two kinds of active surface species (acidic and basic centers) that govern the interaction of the gas phase in contact with the catalyst's surface. Here we will elucidate the cooperative interplay of these two active surface sites for a simple model reaction, namely the water formation over RuO2 catalysts when supplying hydrogen and oxygen from the gas phase. The bridging O atoms harvest the hydrogen from the gas phase, while the on-top O atoms pick up those adsorbed hydrogen atoms from the bridging O atoms to form water. This mechanism of hydrogen transfer is mediated by a strong hydrogen bond. Hydrogen transfer is expected to play a vital role for the whole class of catalyzed hydrogenation and dehydrogenation reactions of hydrocarbons over RuO2.