That was for water and sewer pipe.
That's right. As I said, unfortunately I wasn't able to locate explicit requirements that governed the placement or depth of PVC pipe used in swimming pool installations. Even the provisions of the National Standard Plumbing Code are non-authoritative unless referenced by jurisdictional statute. The recommendations (or standards) excerpted from these sources I took to be relevant for general applications of buried PVC—for water supply, collection, distribution or drainage.
Pool plumbing is treated like sprinkler lines. Since pools are winterized, I could actually run them on the ground, not that I would. When replacing lines, I like to go at least a foot down to avoid issues with lawn aerators.
My knowledge of plumbing and landscaping is limited by my own experience. In the rear yard my sprinkler lines are probably a foot down; the supply and return lines the PB ran from pad to pool are at least 18†below finished grade and in some areas closer to 2 ft. When they were being pressure-tested I noticed that after dropping away from the pad the main lines to pool and spa ran level until they swept up slightly to meet their connections. However small diameter lines used for deck jets, pool overflow and the auto-fill supply all nearly abut the concrete deck poured above them. There’s no frost line here to have to contend with.
What’s a lawn aerator?