Water masers accompanying OH and methanol masers in star formation
  regions
  The ATCA has been used to measure positions with arcsecond accuracy for 379
masers at the 22-GHz transition of water. The principal observation targets
were 202 OH masers of the variety associated with star formation regions (SFR)s
in the Southern Galactic plane. At a second epoch, most of these targets were
observed again, and new targets of methanol masers were added. Many of the
water masers reported here are new discoveries. Variability in the masers is
often acute, with very few features directly corresponding to those discovered
two decades ago. Within our current observations, less than a year apart,
spectra are often dissimilar, but positions at the later epoch, even when
measured for slightly different features, mostly correspond to the detected
maser site measured earlier, to within the typical extent of the whole site, of
a few arcseconds. The precise water positions show that approximately 79% (160
of 202) of the OH maser sites show coincident water maser emission, the best
estimate yet obtained for this statistic; however, there are many instances
where additional water sites are present offset from the OH target, and
consequently less than half of the water masers coincide with a 1665-MHz
ground-state OH maser counterpart. We explore the differences between the
velocities of peak emission from the three species (OH, methanol and water),
and quantify the typically larger deviations shown by water maser peaks from
systemic velocities. Clusters of two or three distinct but nearby sites, each
showing one or several of the principal molecular masing transitions, are found
to be common. In combination with an investigation of correlations with IR
sources from the GLIMPSE catalogue, these comparative studies allow further
progress in the use of the maser properties to assign relative evolutionary
stages in star formation to individual sites.
