You can try to autotrack it, see if that works. First set your scale with a calibration stick or something similar (Track>New>Calibration Tools). Set your videos framerate in clip settings (Video>Clip Settings).

Then create a point mass (Track>New>Point Mass), and hold Shift+Ctrl and then left click the edge of the rising water. This creates a template that Autotracker will attempt to find in each subsequent frame. You can change the shape of it (for instance, make it more flat and wide) and size. Then you can try to autotrack by pressing the "Start" button.

Another tip is that if you are only interested in vertical movement, you can orient the axes such that the x-axis is vertical and then pressing the "x-axis only" option in the Autotracker.

You can also simply track manually by creating a point mass and then Shift+Left click the edge for each frame in your video. If your video has a lot of frames, or you have a lot of videos, this might be tedious, though.