Had the same isue with contaminated water. They can not go deep enought, eventrought I made a clear path with ladders. They can build to a point, but then they can't go back where ther were. Probably because the water raised due to pressure (started digging bellow water level. Is this a protection to keep them from drowning?
Not a bug. This is due to pipes's behaviour. 1. Can the contaminated water extract from the shower fast enought? (may need a few tiles long before next intersection as a buffer). 2. Is there enought water comming in? Same, you might need a small water buffer. may be a bug : Faced with intersections, inputs and outputs have a hard time to do theyr job. Water in OnI will only flow in one direction at a time.