Ratios of the 3600 K/6000 K and 1500 K/3600 K line fluxes, used to investigate the respective strength of each H₂O reservoir. The grey data points are adapted from Banzatti et al. (2025) (see their Table 3), where we have highlighted those analysed by Romero-Mirza et al. (2024) and potential type P sources (i.e. MY Lup, RY Lup and IRAS-04385). The coloured data points indicate the line ratios of our sample of compact discs. See Section 5.1 for a discussion on the different types.