The electron-water heptamer is one of the "magic'' numbers in the mass spectra of electron-water clusters, but up to now the structure of the electron-water heptamer is not known. Thus we have investigated a number of low-energy structures, and report the lowest-energy structure using ab initio calculations. The relative energies, vertical electron-detachment energies, and OH vibrational frequencies of several lowest energy conformers are discussed. As in the case of e(-)(H2O)(6), the electron affinity for e(-)(H2O)(7) is predicted to be positive, which would explain the intense peak observed in the time-of-flight mass spectra. (C) 2003 American Institute of Physics.