Spectra of the 380 GHz H₂O(4₁₄ − 3₂₁) line in APM 08279+5255 and NCv1.143 in red (the green error bar indicates the averaged noise level around the spectra per bin), overlaid with the scaled-down profile of the CO(4 − 3) line. The 380 GHz H₂O line appears narrower by a factor of a few compared with CO(4 − 3), indicating that it is likely associated with maser origins. Black arrows indicate a ∼2 σ satellite line detection, possibly from the H₂O maser, which could originate from accretion disks around the central SMBH.