Comparison of H₂O emission toward several low-mass protostars at long wavelengths in MRS channel 4. B1-a-NS is a Class I source, the other sources are Class 0 sources, including SMM3. The bottom panel shows warm and cold water model spectra at T_rot=370 K (dark blue) and 160 K (light blue). The observed emission in protostars is dominated by the colder component. For comparison, the spectrum of a Class II disk, DF Tau, is shown at the top, illustrating that this disk has strong warm water emission (Grant et al. 2024).