Modeled H₂O line ratios as a function of T_dust (colored lines), compared with the measured ratios (appropriate for the disk, in yellow). The colors indicate the H₂O column densities as indicated in panel b, and solid and dashed lines correspond to τ₁₀₀ = 1.0 and 3.4, respectively. Panel b: the measured F_H2O448/F_H2O248 has been corrected by assuming that 70% of F_H2O448 arises from the disk. While the observed F_H2O212/F_H2O248 ≈ 0.4 ratio in panel a can be explained with a range of T_dust and N_H2O (increasing T_dust with decreasing N_H2O), the measured F_H2O448/F_H2O248 breaks the degeneracy favoring the highest N_H2O and moderate T_dust ≲ 65 K.