The ornamental design for a watermattresssupport, as shown and described.
FIG. 1 is a top plan view of a water mattress support showing my new
design, the bottom being plain and unornamented;
FIG. 2 is a enlarged side elevational view thereof, shown broken-away for
convenience of illustration and with the sides opposite and adjacent being
identical in appearance;
FIG. 3 is an enlarged fragmentary vertical cross-sectional view thereof,
taken along line 3--3 of FIG. 1; and
FIG. 4 is an enlarged fragmentary vertical cross-sectional view thereof,
taken along line 4--4 of FIG. 1.