We introduce the orbital-resolved electron density projected integral (EDPI) along the H-bond in the real space to quantitatively investigate the specific contribution from the molecular orbitals (MOs) aspect in (H2O)(2). Calculation results show that, the electronic occupied orbital (HOMO-4) of (H2O)(2) accounts for about surprisingly 40% of the electron density at the bond critical point. Moreover, the electronic density difference analysis visualizes the electron accumulating effect of the orbital interaction within the H-bond between water molecules, supporting its covalent-like character. Our work expands the understanding of H-bond with specific contributions from certain MOs. (C) 2017 Elsevier B.V. All rights reserved.