Synthetic H₂O(1₁₀−1₀₁) observations for L1551-IRS5, assuming different parameters for the FUV fluxes (G_isrf and G_cr), and velocity profiles (radial velocity v_r and the turbulent broadening Doppler-β) in a sequence from Model A to D. The top row shows the synthetic spectra (red) alongside the observations (black), which have been shifted by the systemic velocity. The middle row depicts the assumed velocity profile, and the bottom row shows the water abundance profile. For comparison, the abundance profile of the preceding model is shown as dashed line.