Ground-state potential energy surface of the CO-H2O system was explored using ab initio calculations at the CCSD(T)/6-311++G**//MP2/6-311++G** level. Providing energy of about 74 kcal/mol, the initial bimolecular complex CO-H2O can associate into formic acid (HCOOH) or dihydroxycarbene (HOCOH). Both HCOOH and HOCOH can further dissociate into CO2 and H-2 through three reaction channels. Providing energy more than 100 kcal/mol, CO-H2O complexes can dissociate into hydroxyl (OH) and formyl (HCO) radicals. Further association of the two radicals leads to formaldehyde carbonyl oxide, dioxirane, and some highly unstable species, including triangular CO2 and linear carbon peroxide COO.