Water maser 3D velocities in IRAS 21078+5211. Colored dots and arrows give water maser positions (relative to the reference feature # 0) and proper motions (relative to the YSO), respectively, with colors denoting the maser V_LSR. We show only the masers for which the position at the first observing epoch can be derived. The amplitude scale for the velocity is reported in the bottom-left corner of the panel. The black dotted rectangles encompass the three regions to the N, NE, and SW of the YSO, where maser emission concentrates. The sky-projected jet and disk axes are in red and black, respectively, with distances labeled in astronomical units. An elongated maser stream directed approximately S-N is traced with a dashed-line segment labeled “B3.”