The potential energy surface of the water trimer has been studied through the use of ab initio quantum mechanical methods. Five stationary points were located, including one minimum and two transition states. Ah geometries were optimized at levels up to the double-zeta plus polarization plus diffuse (DZP+diff) single and double excitation coupled cluster (CCSD) level of theory. CCSD single energy points were obtained for the minimum, two transition states, and the water monomer using the triple-zeta plus double polarization plus diffuse (TZ2P+diff) basis at the geometries predicted by the DZP+diff CCSD method. Reported are the following : geometrical parameters, total and relative energies, harmonic vibrational frequencies and infrared intensities for the minimum, and zero point vibrational energies for the minimum, two transition states, and three separated water molecules.