In this work, we study the interaction between water molecules and a soot surface by means of quantum calculations. The partially oxidized soot is modeled by the anchoring of COOH groups on the face side of a graphite surface. The quantum chemical calculations aim at providing the local structure Of Such a COOH site as well as the surface rearrangements around it. They also provide values of the interaction energies and spectroscopic properties of a hydrogen-bonded water Molecule that could be used for comparison with experimental data. Additionally, the calculations supply values of point charges at the COOH site that can be used to derive a pair potential for the water-active site interaction.