In interstellar media, in which water is present as a major species, OH radicals can form following irradiation by energetic cosmic rays. Laboratory experiments have proved that when water ices are irradiated with energetic particles, OH–(H2O) are formed. Additionally, ground-state OH radicals may exist in the interstellar media, especially in dense interstellar clouds whose outer regions stop energetic particles. To this extent, the understanding of the reactivity of OH radicals in their ground state is of primary importance in the astrochemical context. We experimentally show that the co-injection of an OH radical beam with dilute water molecules leads to the formation of OH–(H2O) complexes on copper rhodiated mirrors maintained at 3.5 K, under a pressure of 10−5 mbar.