Left: best fit to the HIFI data for a Gaussian distribution of H₂O around the equator with y_eq = 7.2 ppb and σ = 25°. The data are shown in black and the model in red; the residuals (observation − model) are plotted at the bottom with the 1σ level of noise in black dashed lines. The synthetic spectrum is too broad and there is a lack of emission at the center. The best-fit model to the PACS data from Fig. 7 is shown in blue for comparison. Right: normalized and beam-averaged contribution functions at the centers of the 66.44 μm line in limb geometry (blue) and at the disk center (green), and of the 1097 GHz line at the disk center (red) are shown. Both functions are computed at their respective observed spectral resolution and the contribution of the continuum emission was subtracted. We note that we rescaled the HIFI contribution function by multiplying it by a factor of 1.45 for an easiercomparison with the PACS value.