The ornamental design for a supportring for a water heater stand, as shown and described.
FIG. 1 is a top perspective view of a support ring for a water heater stand according to the present invention;
FIG. 2 is a top plan view of the support ring of FIG. 1;
FIG. 3 is a bottom plan view of the support ring of FIG. 1;
FIG. 4 is a front side elevation view of the support ring of FIG. 1, and a rear side elevation view being a mirror image of the front side elevation view;
FIG. 5 is a right side elevation view of the support ring of FIG.1, and a left side elevation view being a mirror image of the right side elevation view; and,
FIG. 6 is a top perspective, exploded view of the support ring of FIG. 1.
The broken lines are for illustrative purposes and represent environmental structure and unclaimed portions of the invention and therefore form no part of the claimed design.