Adsorption of H2O on the TiO2(110)-(1 x 2) surface was studied in ultrahigh vacuum (UHV) using the scanning tunneling microscope (STM). At 300 K H2O adsorbs preferentially on the crosslinks of the TiO2(110)-(1 x 2) surface. Cooling down the surface to 110 K during H2O exposure results in adsorption on the crosslinks and other surface sites, presumably the 5-fold coordinated Ti-atoms. The reaction products, observed as bright protrusions at positive sample bias, are attributed to hydroxyl groups due to H2O dissociation. In addition, it was found that the UV-induced line-defects on the TiO2(110)-(1 x 2) surface do not interact with H2O as seen by STM. (C) 2003 Elsevier B.V. All rights reserved.