Orientation of water molecules around ionic arsenic has been studied in detail using density functional B3LYP method. Both trivalent and pentavalent ionic states of arsenic are considered to investigate the orientations. The structure, stability and energetics of the ionic arsenic-water complexes, As3+-nH(2)O (n = 1- 6) and As5+-nH(2)O (n = 3-6) have been investigated with increasing number of water molecules. The change in binding energy (BE) of the arsenic-water complexes has been discussed in detail. Symmetry, hybridization and charge transfer in these complexes have been illustrated with the help of natural electron configuration. Both donation and back-donation processes involving the orbitals of oxygen and arsenic are analyzed to explain the charge transfer. (C) 2011 Elsevier B. V. All rights reserved.