Refrigerator water line under doorway.
If you must put the pipe just under the floor (less than about 1-1/4 inch from the surface), put down a continuous row of nailing plates (nail protection plates, they're something like 1-1/2 inches wide and 3 to 4 inches long) commonly used with electrical wiring so as to cover the pipe's path. Your thicker threshold or other floor trim would go on top of this. Some more elaborate carving will be needed.
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.