  We present Odin observations of the AGB star W Hya in the ground-state
transition of ortho-H2O, 1(10)-1(01), at 557GHz. The line is clearly of
circumstellar origin. Radiative transfer modelling of the water lines observed
by Odin and ISO results in a mass-loss rate of (2.5 +/- 0.5)E-7 Msol/yr, and a
circumstellar H2O abundance of (2.0 +/- 1.0)E-3. The inferred mass-loss rate is
consistent with that obtained from modelling the circumstellar CO radio line
emission, and also with that obtained from the dust emission modelling combined
with a dynamical model for the outflow. The very high water abundance, higher
than the cosmic oxygen abundance, can be explained by invoking an injection of
excess water from evaporating icy bodies in the system. The required extra mass
of water is quite small, on the order of ~ 0.1 earth mass.
