Upper panel: neutral temperature (black curve), total density (red dashed curve), water density (blue dashed curve), and fractional density (blue continuous curve). The so-called fractional density is the water density over the total density, locally defined at each point of the shock. Lower panel: neutral temperature (black curve), total column density (red dashed curve), water column density (blue dashed curve), and fractional column density (blue continuous curve). The so-called fractional column density is the water column density over the total column density. The column density (in cm^-2) is the integral of the local density (in cm^-3) along the shock width (in cm). In both panels, the three points labelled on each curve correspond to the distance parameter of 3.1 × 10¹⁵, 5.15 × 10¹⁵, 10¹⁶ cm, or to time parameters values of 500, 1000, and 2150 yr.