CLOUDY H₂O(3₂₁ − 3₁₂)-normalized SLED models in the PDR (left panels) and XDR regime (right panels), for which we varied the intensity of the incident radiation field over the entire parameter space and for two reference values of total hydrogen density (n_H = 10^2.3, 10^4.6 cm⁻³), and column density N_H = 10²⁴ cm⁻². PDR cases are shown in blue and XDRs are red. They are color-coded according to the values of the radiation field flux. The energy of the upper levels of the 2₂₀ − 2₁₁ and 3₁₂ − 3₀₃ transitions were shifted for clarity to −20 and +20 K, respectively. In order to exclude unphysical models, we report H₂O SLEDs in which the H₂O 3₁₂ − 2₂₁ intensity is > 10⁻²× that of the corresponding CO(10−9) line.