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A radiative transfer method for the treatment of molecular lines ispresented. We apply this method to previous SWAS and ISO observations of watervapor in the source S140 in order to make models to plan for, and to interpret,HIFI data. Level populations are calculated with the use of a three-dimensional(multi-zone) escape probability method and with a long characteristic code thatuses Monte Carlo techniques with fixed directions. Homogeneous andinhomogeneous models are used to compute the differences between water lineprofiles across the S140 region. We find that when an outflow or infallvelocity field with a gradient of a few kms^{-1} is adopted, line profiles witha FWHM of 6 kms^{-1} are found, in agreement with observations. Inhomogeneousmodels are favoured to produce a single-peaked line profile. When zooming in onsmaller regions within the PDR, the shapes of the line profiles start to differdue to the different temperature and density distributions there. The embeddedsources are traced by high excitation lines of, e.g., 3_{21}-2_{21},3_{03}-2_{12}, 2_{12}-1_{01} and 2_{20}-1_{11}. The computed intensities areroughly consistent with existing ISO observations. Water emission in a PDRsource like S140 requires a combination of a pure PDR and an embedded source inorder to match the observations. Because of its good angular resolution, HIFIwill be able to distinguish between a dense star forming region or a morediffuse gas component. It is therefore important for future observing programsto consider both in their predictions of the emission characteristics of waterin these environments.

Line profiles of water for the photon dominated region and embedded sources in the S140 region