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