The adsorption/interaction of KH2PO4 with solvated (100) and (101) TiO2 anatase surfaces is investigated using periodic DFT calculations in combination with GIPAW NMR calculations and experimental IR and solid state O-17, and P-31 NMR spectroscopies. A complete and realistic model has been used to simulate the solvent by individual water molecules. The most stable adsorption configurations are characterized theoretically at the atomic scale, and experimentally supported by NMR and IR spectroscopies. It is shown that H2PO4- chemisorbs on the (100) and (101) anatase surfaces, preferentially via a bidentate geometry. Dimer (H3P2O7-) and trimer (H4P3O10-) adsorption models are confronted with monomer adsorption models, in order to rationalize their occurrence.