The ornamental design for a water bottle for rodent cage, as shown and described.
FIG. 1 is a top view of a design for a water bottle for rodent cage constructed in accordance with the invention;
FIG. 2 is a side plan view of the water bottle for a rodent cage depicted in FIG. 1;
FIG. 3 is a front plan view of the water bottle for a rodent cage of the design depicted in FIG. 1, the opposite rear view being identical thereto in mirror image; and,
FIG. 4 is a perspective view of the water bottle for a rodent cage of the design depicted in FIG. 1.