183 GHz H₂O observations for the RSG stars. Horizontal arrows indicate the velocity extent of 22 GHz (black), 321 GHz (red), and 325 GHz (blue) emission measured by Yates et al. (1995). Note that the 1σ rms sensitivity of the observations by Yates et al. (1995) could be up to 14.2 Jy (in 0.33 km s^-1), so that this should be taken into account when comparing the linewidths. Vertical black arrows indicate the terminal velocity, v_t, estimated for the envelope using low-J CO. For VY CMa, v_t ~ 35 km s^-1 (Decin et al. 2016) and for VX Sgr v_t = 30 km s^-1 (GA98).