Top: comparison of model H₂O line profiles for IRAS4A using the abundance profiles shown in the right-hand panel of Fig. 15 with G_cr varying between 3 × 10^-5 (blue), 10^-4 (red) and 3 × 10^-4 (green). All other variables use the best-fit values. Bottom: comparison of model H₂O line profiles for IRAS 15398 with G_isrf = 0 (red) and G_isrf = 1 (blue). The green error bar and scaling factors are the same as in Fig. 6.