Nominal water vertical profiles used in the analysis of the HIFI and PACS maps. The IDP profile (red solid line) was computed with the photochemical model of Cavalié et al. (2008b), using the nominal thermal profile of Fig. 6 and a standard K(z) profile from Moses et al. (2005). In the SL9 profile, a cut-off level was set to p₀ = 2 mbar. This is the highest value of p₀ that enables reproducing all the HIFI lines. In this profile, the water mixing ratio is 1.7 × 10^-8 as in the central pixel (number 13) of the HIFI map.