Since 1973, the 18-cm lines of the OH radical have been systematically observed in a number of comets with the Nançay radio telescope. This allowed an evaluation of the cometary water production rates and their evolution with time, as well as a study of several physical processes: the excitation mechanisms of the OH radio lines, the expansion of the cometary atmospheres, their anisotropy in relation with non-gravitational forces, the Zeeman effect in relation with the cometary magnetic field. The Nançay observations of 53 cometary apparitions between 1982 and 2009 are now organized in this database.