  VLBI multi-epoch water maser observations are a powerful tool to study the
gas very close to the central engine responsible for the phenomena associated
with the early evolution of massive protostars. In this paper we present a
summary of the main observational results obtained toward the massive
star-forming regions of Cepheus A and W75N. These observations revealed
unexpected phenomena in the earliest stages of evolution of massive objects
(e.g., non-collimated "short-lived" pulsed ejections in different massive
protostars), and provided new insights in the study of the dynamic scenario of
the formation of high-mass stars (e.g., simul- taneous presence of a jet and
wide-angle outflow in the massive object Cep A HW2, similar to what is observed
in low-mass protostars). In addition, with these observations it has been
possible to identify new, previously unseen centers of high-mass star formation
through outflow activity.
