On top there is the used-water and the available-water.

The release of the trooper stops as long as there is not enough water
(trooper needs 1 waterunit)
You can build units, but they are only spawned whenever there is enough water available.
you need to build more waterwells then.

The troups share a calculated path for speed reasons,
so sometimes a unit tries to go one step back to start the pathfollowing.
I have to see how to improve that.