Comparison between the opacities derived with (solid lines) or without (dashed lines) accounting for maser propagation for the masers at 22 GHz, 380 GHz, and 448 GHz. The left column corresponds to a cut in density at n(H₂) = 2    ×    10⁷ cm^-3; the differences are shown with respect to variations in X(H₂O). The right column corresponds to a fixed water abundance, i.e. X(H₂O) = 4    ×    10^-4.