What is the purpose of a trap in a plumbing system?

The purpose of a trap in a plumbing system is fundamentally to prevent sewer gases from entering a building. Traps are curved sections of drain pipes designed to hold a small amount of water at all times. This water acts as a barrier against harmful gases and odors that can come from the sewer. By maintaining this water seal, traps ensure that noxious fumes can escape into the living spaces of a structure, thereby protecting the health and comfort of its occupants.

While traps do play a role in drainage and plumbing function, their primary and most critical function is safeguarding indoor air quality by blocking sewer gas infiltration.