What is one of the primary functions of a trap in a plumbing system?

The primary function of a trap in a plumbing system is to seal against sewer gases. Traps are designed to hold a small amount of water at all times, creating a barrier that prevents noxious gases from the sewer system from entering the living spaces of a building. This water seal is crucial in maintaining indoor air quality and ensuring a safe and pleasant environment.

When waste water flows into the trap, it displaces the water already present, but as soon as the flow stops, the water in the trap remains, effectively blocking gases from escaping through the drain. This is essential for health and safety, as sewer gases can be harmful and odoriferous.

Understanding this function highlights the importance of properly maintaining traps in plumbing systems, as a malfunctioning trap can lead to sewer gas odors and potential health hazards. The other options refer to functions that are not related to traps. For instance, pressure relief and distribution of hot water pertain to different components in plumbing systems, while measuring water flow is typically associated with flow meters rather than traps.