Sometimes, if I create a T-junction (for example, to divide water coming from one pump to a shower and a lavatory) and later delete one of the sides (leaving just an L-bend), half the water blobs that reach the bend disappear.
This seems to be because the game treats pipes as two different "entities": a pipe actually present at the tile, and a connection across each of the tile's boundaries. Deleting the pipe from a tile sometimes seems to leave a "ghost" of the connection from the previous tile, so the blobs keep getting moved across the tile boundary, but into a tile that now doesn't contain an actual pipe. Result, the liquid gets deleted.
This might be the actual cause of some devices (pumps, filters, etc.) deleting liquids after the pipes around them are edited (although there also seem to be other bugs with the devices themselves).
1. Build pump, place a T-junction on the outgoing pipe, with each side connected to a different building. Let the pump run, confirm that water is being sent to both sides. 2. Delete the segment of pipe immediately after the junction, on one side, leaving an L-bend. 3. If the bug was triggered, one out of every two blobs of water disappears when it reaches the bend.