On my morning dog walk I have had some conversations with a plumber working on a total slab up rebuild of a burned house. All copper water lines below the slab are being abandoned. The new water lines will be PEX.
He is bringing the cold water main supply into the house through a conduit of PVC Schedule 80. Looks like 3 inch, but I don't really know. He hired laborers to tunnel under the slab to a front half bathroom. There is a horizontal run of this PVC from a few feet outside the slab then a long sweep elbow to a vertical run of PVC coming through a hole in the slab. He fed the PEX line through this conduit. From there all piping will be in the walls, inter-floors space, and attic.
Should the incoming water line ever leak, one could pull the leaking line out and feed a new PEX line in.