Use the water drop utility to trace the path that water takes across a surface.
The utility draws a 2D or 3D polyline that represents a flow of water and also marks the start point of the path. If a channel splits, then new polylines are drawn to follow each water drop path.
For example, multiple water drop paths can be drawn from a contour line to illustrate the water flow at different points along the contour:

You can use either a 2D or 3D polyline to draw the flow line. The line type that you use depends on your analysis requirements. Following are usage examples for each line type:
- 2D polyline. Delineate an area that represents a drainage area for water runoff analysis. You create a closed 2D polyline using AutoCAD editing commands. You can use the resulting closed 2D polyline to query the area and perform other analysis.
- 3D polyline: You want to perform visualization and drape the lines over the surface. You can also create grading feature lines from the water drop lines for grading purposes.