  Water masers have been observed in several high redshift active galactic
nuclei, including the gravitationally lensed quasar MG 0414+0534. This quasar
is lensed into four images, and the water maser is detected in two of them. The
broadening of the maser emission line and its velocity offset are consistent
with a group of masers associated with a quasar jet. If the maser group is
microlensed we can probe its structure and size by observing its microlensing
behaviour over time. We present results of a high resolution numerical analysis
of microlensing of the maser in MG 0414+0534, using several physically
motivated maser models covering a range of sizes and emission profiles.
Time-varying spectra of the microlensed maser are generated, displayed, and
analysed, and the behaviour of the different models compared. The observed
maser line in MG 0414+0534 is consistent with maser spots as in other quasar
jets, provided substructure is de-magnified or currently lost in noise;
otherwise smooth extended maser models are also candidates to generate the
observed spectrum. Using measures of spectral variability we find that if the
maser has small substructure of ~ 0.002 pc then a variation of 0.12 mag in flux
and 2.0 km/s in velocity centroid of the maser line could be observed within 2
decades. For the smallest maser model in this study a magnification of > 35 is
possible 22% of the time, which is of significance in the search for other
lensed masers.
