I accidentally pumped in PW into my Air Mesh walled Water reservoir and was surprised to see both Water and PW come flooding out of the right side. As this moment this could be used to filter PW out out of Water reservoirs if players don't mind Mopping up a mess.
There has always been a problem in the game where PW forces itself into Air Mesh tiles on the (bottom) right while regular Water when loading a game forces itself through the (bottom) left. At this moment Air Mesh tiles don't truly do as described. They block liquids, but if a liquid somehow enters an Air Mesh tile it either forces it out or the liquid becomes trapped if blocked by other Air Mesh tiles.
Steps to Reproduce
Save included. Just wait until the PW enters the reservoir and the mix of Water and PW will flood out. Cancel the pipe destruct order and just watch the pump send the PW to the Water reservoir.
This issue has not been confirmed by a developer yet.