H₂O lines in the red band (λ > 100 μm) detected in NGC 4418 (upper spectra in each panel) and Arp 220 (lower spectra). The spectra have been scaled by a factor of 2 in panels a), k) and l), and by 3 in panel c). Model results are also shown. Color codes for the contributions of the different components are given in Fig. 3, with the yellow curve in panel q) showing the additional contribution by the halo component (C_halo) in front of the nuclear region of Arp 220.