What do we call a manufactured device or assembly that does not require additional water supply but performs useful functions in plumbing?

A manufactured device or assembly that does not require an additional water supply but serves a useful function in plumbing is referred to as plumbing appurtenances. This term encompasses various components that enhance the plumbing system's performance and functionality without necessitating a separate connection to the water supply.

Plumbing appurtenances can include items such as backflow preventers, which help protect the potable water supply, or clamps and hangers that support piping. These devices are crucial in ensuring a safe and efficient plumbing system, and they contribute to the overall operation of plumbing without needing extra water input.

In contrast, utility devices typically relate more to equipment that requires some form of energy or water supply to operate. Supporting equipment generally refers to items that aid in the overall function of the plumbing system but aren't classified in the same specific way as appurtenances. Supplementary fixtures might suggest additional fixtures that require water, which does not align with the question's focus on devices that do not need an additional water supply.