Models of H₂O population level diagrams (upper and lower panel, respectively, for ortho- and para-H₂O) for our three quasar host galaxies. Each of the model shows the level volume density (weighted with their quantum degeneracy) at the N_H2O, τ₁₀₀, and T_dust values corresponding to the MOLPOP-CEP best-fit H₂O SLED models (see Sect. 7.2). The straight lines are the analytical population diagrams computed assuming Boltzmann distribution color-coded by the excitation temperature. The green line corresponds to the LTE case (T_kin = T_ex).