The ornamental design for a waterpurifier, as shown and described.
FIG. 1 is a front view of a water purifier showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines in FIG. 1 represent the trademark and form no part of the claimed design. The broken lines in FIGS. 2 and 6 form no part of the claimed design.