Based on first-principles total energy calculations, we demonstrate that two water molecules encapsulated in the C-60 dimer form a peculiar tail-to-tail dipole arrangement that is energetically unfavorable in classical electrodynamics. This arrangement is ascribed to charge depression at the wall of C-60 associated with [2 + 2] cycloaddition in the dimer structure resulting in a decrease of the energy cost of Coulomb repulsive interaction in the arrangement. First-principles molecular dynamics simulations also show that the water molecules retain the peculiar arrangement up to the temperature of about 10 K. (C) 2014 Elsevier B.V. All rights reserved.