The ornamental design for a petwaterfountain, as shown and described.
FIG. 1 is a perspective view of a pet water fountain showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is an enlarged view of detail area 9 circumscribed within FIG. 1.
The broken lines and all areas within depict portions of the pet water fountain that form no part of the claimed design. The dot dash dot broken lines in FIG. 1 and surrounding FIG. 9 denote the boundaries of the detail area and form no part of the claimed design.