G2 ab initio molecular orbital calculations have been carried out to study the potential energy surfaces (PESs) associated with the reactions of Cl+ in its P-3 ground state and in its D-1 first excited state with water. Similar to what was found for the reactions involving F+, the [H-2,Cl,O](+) triplet state cations are weakly bound species, while the corresponding singlets are covalently bound species. As a consequence, although the PES of Cl+(P-3) lies 33.0 kcal/mol below that of the Cl+(D-1), the global minimum of the singlet potential energy surface lies 34.0 kcal/mol below the global triplet minimum. We have also found significant differences between the [H-2,Cl,O](+) species and their fluorine-containing homologs regarding both their pending and relative stabilities. These differences are more pronounced in the case of the triplets where the relative stabilities of the [H-2,F,O](+) minima are completely reversed when fluorine is replaced by chlorine. As a result, most of the products of the reactions of F+ with water cannot be formed in Cl+ + H2O reactions, although also in this case the most likely process is the single charge transfer, in agreement with the experimental evidence. However, the formation of OH+ becomes exothermic when Cl+ reacts in its D-1 excited state. The estimated heat of formation for the most stable H2OCl+ singlet state species is 193 +/- 2 kcal/mol.