  We report the results of observations of ten rotational transitions of water
vapor toward the carbon-rich AGB (asymptotic giant branch) star IRC+10216 (CW
Leonis), carried out with Herschel's HIFI instrument. Each transition was
securely detected by means of observations using the dual beam switch mode of
HIFI. The measured line ratios imply that water vapor is present in the inner
outflow at small distances (few x 1.E+14 cm) from the star, confirming recent
results reported by Decin et al. from observations with Herschel's PACS and
SPIRE instruments. This finding definitively rules out the hypothesis that the
observed water results from the vaporization of small icy objects in circular
orbits. The origin of water within the dense C-rich envelope of IRC+10216
remains poorly understood. We derive upper limits on the H2-17O/H2-16O and
H2-18O/H2-16O isotopic abundance ratios of ~ 5.E-3 (3 sigma), providing
additional constraints on models for the origin of the water vapor in
IRC+10216.
