Over the past decade we observed a sample of late-type stars (supergiants, semi-regular variables, OH/IR stars, and Mira's) 3-4 times per year in the 1.3-cm line of H2O. The observations were carried out with the Medicina 32-m and the Effelsberg 100-m telescopes. In addition, a sub-sample of these stars was observed at several epochs with the VLA. In our analysis we also use data from the literature, for instance on mass loss and optical variability. The aim is to investigate the properties of the circumstellar outflows and to elucidate the maser-pumping mechanism. In the conference poster we presented some preliminary results of a 4-star sub-set of the data base; in the small space available here, we briefly describe the monitoring program, and discuss the Mira-variable R Cas in some detail.