From Equation (12) page 13 we have the following chemical reaction network.
We quote from the reference.
when X1 = H2, X2 = O2, and X3 = H2O, the reversible creation of a molecule of water, when two molecules of the diatomic hydrogen gas combine with one molecule of the diatomic oxygen gas to produce two molecules of water. (The forward reaction produces energy, and the reverse reaction, breaking water to form hydrogen and oxygen, requires energy, for instance through electrolysis. The chemical reaction formalism used here does not account for energy production or consumption.)