It's possible to create a coordinate system. First, make 2 items labeled 'up' and 'down'. Then, create an 'up' job which increases up by 1 and decreases down by 1. The down job will do the opposite. Now, if you want the creek to be from y = 10 to y = 20, you can add 10 up and -20 down to the input of 'Gather Fresh Water'. Add 10 up and -20 down to output to stop your location from resetting. Repeat everything for x coordinates to make it 2D, but make it 1 or 2 wide.
Also, it's kinda already possible to define starting conditions. Add an item called 'start'. Then, add a job called 'first'. First has a job input of 0 start, and an output of -1 start plus whatever items you start with. As long as nothing increases start, you can never use it again. But as a trade off, it adds more pointless clutter.