Water treatment device
The ornamental design for a water treatment device, as shown and described.
 FIG. 1 is a front perspective view of the water treatment device;
 FIG. 2 is a rear perspective view thereof;
 FIG. 3 is a front elevational view thereof;
 FIG. 4 is a back elevational view thereof;
 FIG. 5 is a right elevational view thereof;
 FIG. 6 is a left elevational view thereof
 FIG. 7 is a top plan view thereof; and,
 FIG. 8 is a bottom plan view thereof.
 The broken lines immediately adjacent to the shaded portions form the boundaries of the claim. The remaining broken lines show portions of the water treatment device. The broken lines form no part of the claimed design.