From left to right panels: dust temperature structure T_dust(r, z/r) from ProDiMo models for a 0.03 M_⊙ disk 0.2 Myr, 1 Myr, and 10 Myr in age. White dashed lines identify the (T, n_H2O) parameters space called a “box” and analyzed in this work. The insets show the logarithmic scale of water vapor density n_H2O as a function of T_dust. Within the “box” it ranges between 10⁹ and 10¹³ cm⁻³.