High angular resolution (0.07'') observations of the water masers in the circumstellar shells of the supergiant stars VY CMa and VX Sgr and four M giant stars (IK Tau, RT Vir, W Hya, and RX Boo) are presented. For all these sources, the standard spherically symmetric expanding shell model fails to fit the water maser data as well as it fits 1612 MHz OH maser data. A component of radial outflow appears to be present in the H2O shells of three stars (RT Vir, IK Tau, VX Sgr). This and the comparable velocity ranges of H2O and OH masers for each star indicate that at least some parcels of gas are accelerated nearly to the terminal outflow velocity at or inside the radius of the H2O shell. The maser distributions generally are quite asymmetric relative to the estimated stellar positions. The absolute positions of the water masers toward these stars have been determined with a rms accuracy of about 0.1'' and the estimated stellar positions agree with astrometric optical positions at this level of accuracy. For IK Tau and W Hya, the maps of H2O maser features have been compared with other observations of similar angular and spectral resolution at similar phases of their light curves. These are the first such detailed comparisons of water maser maps for circumstellar envelopes. In the case of IK Tau, the agreement of positions and velocities in the maps obtained from these data and data taken a year earlier is quite good. On the other hand, although the similarity of the spectra is striking, maps of water masers for W Hya presented here show little correspondence with data taken five years later, indicating that significant changes in the angular distributions of H2O Masers Can occur over time scales larger than a few years.
