H₂O-to-CO line ratios and, from left to right, bolometric temperature, bolometric luminosity, and envelope mass. The ratios are calculated using lines at nearby wavelengths for which the same, limited to the central spaxel, extraction region is considered. Shown are line ratios of the H₂O 2₁₂ − 1₀₁ line at 179 μm and CO 16−15 at 163 μm (top), the H₂O 4₀₄ − 3₁₃ and CO 21−20 lines at about 125 μm (middle), and the H₂O 2₂₁ − 1₁₀ and CO 24−23 lines at about 108 μm (bottom). Red and blue symbols correspond to sources with T_bol ≤ 70 and >70 K, respectively. Black crosses are drawn for the sources with detections of CO 29−28 line.