Herschel observations of EXtra-Ordinary Sources (HEXOS): Observations of
  H2O and its isotopologues towards Orion KL
  We report the detection of more than 48 velocity-resolved ground rotational
state transitions of H2(16)O, H2(18)O, and H2(17)O - most for the first time -
in both emission and absorption toward Orion KL using Herschel/HIFI. We show
that a simple fit, constrained to match the known emission and absorption
components along the line of sight, is in excellent agreement with the spectral
profiles of all the water lines. Using the measured H2(18)O line fluxes, which
are less affected by line opacity than their H2(16)O counterparts, and an
escape probability method, the column densities of H2(18)O associated with each
emission component are derived. We infer total water abundances of 7.4E-5,
1.0E-5, and 1.6E-5 for the plateau, hot core, and extended warm gas,
respectively. In the case of the plateau, this value is consistent with
previous measures of the Orion-KL water abundance as well as those of other
molecular outflows. In the case of the hot core and extended warm gas, these
values are somewhat higher than water abundances derived for other quiescent
clouds, suggesting that these regions are likely experiencing enhanced
water-ice sublimation from (and reduced freeze-out onto) grain surfaces due to
the warmer dust in these sources.
