The ornamental design for a supportstand for a water treatment assembly, as shown and described.
FIG. 1 is a top and left side perspective view of a support stand for a
water treatment assembly showing my new design, the broken-line showing of
the faucet and water treatment assembly being for illustrative purposes
only and forming no part of the claimed design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a top plan view thereof, the undisclosed bottom being plain and
unornamented; and
FIG. 5 is a left side elevational view thereof, the right side being a
mirror image.