The ornamental design for a waterpurifier, as shown and described.
FIG. 1 illustrates a front perspective view of a water purifier showing my new design;
FIG. 2 illustrates a front elevational view thereof;
FIG. 3 illustrates a rear elevational view thereof;
FIG. 4 illustrates a left side elevational view thereof;
FIG. 5 illustrates a right side elevational view thereof;
FIG. 6 illustrates a top plan view thereof; and,
FIG. 7 illustrates a bottom plan view thereof.
The broken lines showing of a water purifier is included for the purpose of illustrating portions of the article and form no part of the claimed design.