What is the primary purpose of a plumbing fixture trap?

The primary purpose of a plumbing fixture trap is to prevent sewer gases from entering buildings. Traps are designed to hold a small amount of water, creating a seal that effectively blocks the passage of harmful gases that emanate from the sewage system. This water seal is crucial for health and safety, as it helps maintain indoor air quality and prevents unpleasant odors from infiltrating living or working spaces.

In contrast, options relating to blocking water flow, maintaining water pressure, or filtering contaminants do not accurately capture the primary function of a trap. While traps might influence water movement in some contexts, their essential role is focused on creating a barrier against gases rather than managing water flow or pressure. Likewise, while some plumbing components are designed to filter contaminants, traps specifically aren’t meant for filtration—they serve solely to create a seal against harmful gases.