Water masers in bowshocks: Addressing the radiation pressure problem of
  massive star formation
  Ejection activities in S255IR-SMA1 and AFGL 5142 were investigated by
multi-epoch VLBI observations of 22 GHz water masers, tracing bowshocks leading
collimated jets. The history of ejections, revealed by the 3D maser motions and
supplemented by the literature, suggests that these massive stars formed by
episodic accretion, inferred via the accretion-ejection connection. This
contribution centers on the role of episodic accretion in overcoming the
radiation pressure problem of massive star formation - with maser VLBI and
single-dish observations providing essential observational tools.
