Example of radio thermal jet (VLA–1) with nearby knot (VLA–2): H₂O maser site G012.91−0.26 or W33A (Sect. 4.4). Labels and symbols as in Fig. 1. Two radio continuum sources are detected at both C and K bands along a position angle of approximately 152° (panel a): the brightest emission coincides in position with the brightest millimeter source in the dusty core MM1. Panelsb and c: we fitted the spectral index of sources VLA–1 and VLA–2 with the measured fluxes at C and K bands, after dividing the K-band observations into two sub-bands, each spanning 4 GHz. Panelb: fluxes reported in the literature at X (pink), Ku (red), and Q (cyan) bands are consistent with a single linear slope, i.e., from 4 to 43 GHz. The radio continuum emission associated with W33A–MM1 can be interpreted as a thermal jet, whose components VLA–1 and VLA–2 indicate the ionized gas closest to the driving source, namely, MM1-main, and a knot of shocked gas along the jet direction, respectively.