H₂O fluxes and acceptable parameter space of temperature and H₂ density. The upper left panel shows that in the H12 model, all far-IR H₂O lines expected to be strong are detected (red dots), while those expected to be weak are undetected (black dots). Several lines at  ~100 μm were likely undetected because the S/N is degraded in that wavelength region. The upper middle panel shows the acceptable contours for flux ratios of o-H₂O 8₁₈−7₀₇/7₀₇−6₁₆ (blue), o-H₂O 7₀₇−6₁₆/6₁₆−5₀₅ (red), and both (purple), for two different column densities. The acceptable parameter space shows the 1σ error bars with a 20% relative flux calibration uncertainty. The lower left panel shows that the non-detection of the o-H₂O 5₅₀−5₄₁ and 6₅₂−6₄₃ lines relative to o-H₂O 6₁₆ − 5₀₅ line places a limit on the optical depth of the slab. The lower middle panel shows where the flux ratio of o-H₂O 8₄₅−7₃₄ 35.669 μm to o-H₂O 7₀₇−6₁₆ 71.947 μm is equal to the observed value of 0.07. The lower right panel shows the parameter space (high density and high column density) ruled out by the non-detection of the o-HO 3₂₁ − 2₁₂ line, for four different temperatures.