1996A&A...311..971C

The results of a survey of 22.2GHz water maser emission toward 39 young stellar objects (McCutcheon et al. 1991) are presented. The sample contains bright IRAS sources associated with molecular clumps, which may represent different phases of the early evolution of star forming regions, depending on the presence or absence of compact H II regions. We associate 19 water masers with the IRAS sources, 4 of which are new detections. Taking into account also previous detections of masers that were quiescent during our survey, the total number of sources which show maser emission is 22 (56% of the whole sample). This has to be taken as a lower limit if variability of the maser emission is considered. The maser percentage does not change for sources with or without a compact H II region. It is higher (68%) if we consider only sources associated with large CO linewidths. Our H₂O observations confirm that water masers can occur at the earliest phases of the formation of high luminosity stars, much before the development of an ionized region detectable in the radio continuum, and that they are closely connected with molecular outflows.