Isocontours of the o–H₂O opacities at line centre for the 6₁₆ − 5₂₃ line at 22 GHz, the 4₁₄ − 3₂₁ line at 380 GHz, and the 4₂₃ − 3₃₀ line at 448 GHz. The left column corresponds to the models where the treatment of maser propagation is omitted and the right column to the current results (see text). The isocontour values and the correspondence between grey scale and opacity values are displayed at the top of the two columns. The isocontours that correspond to opacities of − 4 and − 40 are displayed in thick blue lines. Negative values for the opacity correspond to red lines.