22 GHz water masers in IRAS 21078+5211 and a 3D view of the DW streamlines that best reproduce the maser kinematics. (a) Water masers found in the global VLBI observation in 2020 October. Colored dots give the relative positions of the 22 GHz water masers, with colors denoting the local-standard-of-rest velocity of the masers, V_LSR. We note that the observed positions have been rotated 50° clockwise so as to align the jet axis with the vertical axis (and the disk axis with the horizontal axis). The black dotted rectangles encompass the three regions, to the N, NE, and SW, where the maser emission concentrates. The black, red, and blue curves denote the sinusoids drawn by the masers belonging to the SW, NE-2, and NE-3 streams, respectively. (b) Simulation of the DW kinematics. The colored curves denote four DW streamlines departing from the launch radius of 4 au at 90º azimuthal separation from one another, as computed with the simulation that best reproduces the geometry and kinematics of the maser patterns (see Sect. 3.3). Colors show V_LSR using a scale similar to that of the observations. The simulations reproduce only the inner maser streams, within a radius of 40 au. The streamlines labeled “A”, “B”, and “C” are those that best reproduce the NE-3 (blue sinusoid), NE-2 (red sinusoid), and SW (black sinusoid) maser streams, respectively. We note that the NE-2 stream is, strictly speaking, better reproduced using a slightly larger launch radius of 4.5 au (see Sect. 3.3). In agreement with previous observational constraints (see Sect. 3.1), V_LSR is calculated for a LOS inclination of the jet axis of 10º.