A pool is a large volume of chemically treated water, and the fill line is the connection between it and the house.
The hazard is straightforward — chlorinated and stabilized pool water is not drinking water, and a pool with an automatic fill has a permanent connection rather than a hose somebody remembers to disconnect. Spas add heat and a higher chemical concentration in a smaller volume.
The cleanest protection on a fill line is often an air gap, which is not an assembly at all — just a physical break between the fill outlet and the highest water level, with nothing to test and nothing to fail. Where an air gap is not practical, this is health hazard territory.
Scope on this one depends on where the assembly is. On an outdoor equipment pad we handle it end to end — test, repair, replace, install. In an indoor pool or spa room we test and repair, but replacement inside the foundation is licensed plumbing work. The device types, and where our work stops.
Schedule a backflow test or call 970-835-9661