  Several radio sources have been detected in the HMSFR W75N(B), among them the
massive YSOs VLA1 and VLA2 are of great interest. These are thought to be in
different evolutionary stages. In particular, VLA1 is at the early stage of the
photoionization and it is driving a thermal radio jet, while VLA2 is a thermal,
collimated ionized wind surrounded by a dusty disk or envelope. In both sources
22 GHz water masers have been detected in the past. Those around VLA1 show a
persistent distribution along the radio jet and those around VLA2 have instead
traced the evolution from a non-collimated to a collimated outflow over a
period of 20 years. By monitoring the polarized emission of the water masers
around both VLA1 and VLA2 over a period of 6 years, we aim to determine whether
the maser distributions show any variation over time and whether the magnetic
field behaves accordingly. The EVN was used in full polarization and
phase-reference mode to measure the absolute positions of the masers and to
determine both the orientation and the strength of the magnetic field. We
observed four epochs separated by two years from 2014 to 2020. We detected
polarized emission from the water masers around both the YSOs in all the
epochs. We find that the masers around VLA1 are tracing a nondissociative shock
originating from the expansion of the thermal radio jet, while the masers
around VLA2 are tracing an asymmetric expansion of the gas that is halted in
the northeast where the gas likely encounters a very dense medium. We also
found that the magnetic field inferred from the water masers in each epoch can
be considered as a portion of a quasi-static magnetic field estimated in that
location rather than in that time. This allowed us to study locally the
morphology of the magnetic field around both YSOs in a larger area by
considering the vectors estimated in all the epochs as a whole.
