Top panels: line profile versus observation for three different modellings. The best fit model is shown in red. In the left panel, the abundance value at 13 000 AU varies between 6.7 × 10^-8 and 1.3 × 10^-7 and for the right panel, the abundance value at 20 000 AU varies between 5.3 × 10^-8 and 8 × 10^-8. Bottom panel: H₂O abundance profile used for these respective models as a function of the radial distance from the core in arcsec (top axis) and AU (bottom axis).