The ornamental design for a waterbottle, as shown and described.
FIG. 1 is a perspective view of a water bottle;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left elevational view thereof;
FIG. 5 is a right elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The dashed or broken lines shown in the drawings depict portions of the water bottle in which the design is embodied that form no part of the claimed design.