Each plot shows the histogram of the PM PA (0° ≤ PA ≤ 180°) for a specific POETS target, whose name is reported on the top together with the number of PMs employed to produce the histogram. The histogram bin is 20° and the histogram values are normalized by the number of PMs. The average error on the PM PA is ≤10° for most of the sources. The vertical blue line marks the PA of the preferential direction of the water maser PMs, PD_PM (see Sect. 2.4), using filled or dot-dashed lines for more or less collimated cases, respectively. In sources where the presence of a jet has been established through observations of thermal line or continuum tracers, the jet PA from the literature, A_LJ, is denoted by a vertical black dashed line.