Using the Very Large Array ( VLA ) of the National Radio Astronomy Observatory in the A and B configurations , we have obtained simultaneous high resolution observations of both the 22 GHz H _ { 2 } O maser lines as well as the 22 GHz continuum for the H ii regions W49N and Sagittarius B2 .
The angular resolution of both observations is \sim 0 \farcs 1 , which at the distance of W49N ( 11.4 kpc ; Gwinn , Moran , & Reid 1992 ) and Sgr B2 ( 8.5 kpc ) corresponds to a physical size of < 1000 AU in both sources .
The velocity coverage for W49N is \pm 435 km s ^ { -1 } ; positions for 316 H _ { 2 } O maser components were obtained .
The velocity coverage for Sgr B2 is -40 to +120 km s ^ { -1 } ; positions for 68 maser components were determined in Sgr B2 Main , 79 in Sgr B2 North , 14 in Sgr B2 Mid-North , and 17 in Sgr B2 South , for a total of 178 H _ { 2 } O maser positions in Sgr B2 .

The cross calibration scheme of Reid & Menten ( 1990 , 1997 ) was used .
Using this procedure , high dynamic range continuum images were obtained with accurate registration ( \sigma \sim 0 \farcs 01 ) of the continuum and maser positions .
A detailed comparison between H ii components and maser positions for both Sgr B2 and W49N is presented .
In Sgr B2 Main , the H _ { 2 } O masers are predominantly located at the outside edge of the high-frequency continuum , lending support to the proposal that entrainment by stellar winds may play an important role in H _ { 2 } O maser emission .