So I was messing about in the latest release of 1.13 Snapshot (18w10d) I noticed the water flowing from the closed off area from the stairs back is making the flowing water go right out of it. It's a bit weird that is happening from a closed-off part of stairs back cause that isn't supposed to do that cause that doesn't happen in real life but I think that could be just a water mechanic issue that has not been implemented yet but I do hope it gets fix very easily.