What you can do after the plumber leaves is to install some plastic above the layout where the pipes are so it can keep the water off your layout.
I had a milk leak many years ago when I lived in Stratford CT, my mom spilled a half gallon of milk in the kitchen and it came through the ceiling and got some freight cars. I still can't get the stuff off the freight cars, so they have what looks like water damage on them.
Lee Fritz
