The gas-phase reaction of the Al-6(+) cation with a water molecule is investigated computationally by coupled cluster and density functional theories. Several low-energy paths of the mechanism for dihydrogen production from H2O by the positively charged aluminum cluster are identified. This reaction involves the initial formation of the association complex, exothermic by 25 kcal/mol, followed by the water dissociation and H-2 elimination major steps, yielding the Al-6(+) product oxide with either the nonplanar or planar structure. The 1-120 dissociation on Al-6(+) is the rate-determining step. Of the paths probed, the one kinetically most preferred leads from the O H bond dissociation transition state lying below the separated reactants to the immediate HAl6OH+ intermediate of the "open" type and involves further the more compact intermediate from which Hy is eliminated. The other reaction paths explored involve the activation enthalpy (at 0 K) for the rate-determining step of less than 2 kcal/mol relative to the Al-6(+) H2O. Natural population analysis based charges indicate that forming of Hy along the elimination coordinate is facilitated by the interaction of the hydridic and protic hydrogens. For the kinetically most favorable route detected, the coupled cluster singles and doubles with perturbative triples (CCSD(T)) relative energies calculated with the unrestricted and restricted HF references are in a good agreement. This investigation is relevant specifically to the recent mass spectrometric study of the reactivity of Al-n(+) with water by Arakawa et al., and it provides a mechanistic insight into the formation of the observed AlO+ product oxide with n = 6.