  We report high spatial and spectral resolution measurements of masers towards
R Aqr and H1-36, both of which are examples of the sub-class of symbiotic stars
that contain a long-period Mira-type variable. Our observations have resulted
in the first detection of 321-GHz H2O maser action towards a symbiotic Mira - R
Aqr. Comparison with simultaneous 22-GHz H2O maser data suggests the masers do
not have the same properties as those in the circumstellar envelopes of field
Miras. R Aqr's 22-/321-GHz peak flux density and luminosity ratios are low, as
is the line-width ratio. Continuum and spectral-line maps indicate that the
22-GHz maser and free-free emission are aligned. Three mechanisms can reproduce
the data with varying degrees of success. All three lead naturally to normal
levels of maser emission in SiO and 321-GHz H2O and anomalously weak OH and
22-GHz H2O masers. In the most convincing model, UV radiation and a fast wind
from the companion remove the Mira's envelope of dusty, molecular gas, leaving
a relatively small cavity of dense, neutral material within a large, ionized
nebula. Excitation temperatures suggest that 321-GHz masers are normally
excited close to the Mira whilst 22-GHz masers are more remote; in R Aqr,
therefore, the 22-GHz masers do not form under optimum conditions. Instead, we
see weak and narrow lines that form closer to the Mira, consistent with our
high-resolution maps.
