Top: ratio between H₂O 2₁₂ − 1₀₁ (179 μm) and 3₀₃ − 2₁₂ (174 μm) emission, as a function of T for two values of H₂ density (n_H2 = 5 × 10⁵ cm^-3 and 5 × 10⁶ cm^-3) and two values of H₂O column density (N_H2O = 3 × 10¹⁴ and 4 × 10¹⁵ cm^-2) of L1448-B2. The shaded band highlights the H₂O ratio observed with PACS and the arrows indicate that this ratio can be considered an upper limit (see text for details). Middle and bottom: ratios between H₂O 3₀₃ − 2₁₂ (174 μm) and 3₁₃ − 2₀₂ (138.5 μm) emission and between H₂O 3₀₃ − 2₁₂ (174 μm) and 4₀₄ − 3₁₃ (125.4 μm) emission, respectively, as a function of T. The symbols are the same as in the top panel.