The ornamental design for a waterkettle, as shown and described.
FIG. 1 is a perspective view of a water kettle according to the claimed design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is another perspective view of the water kettle according to the claimed design.
The broken lines showing portions of the water kettle are for the purpose of illustrating environmental structure only and forms no part of the claimed design.