What is the purpose of a trap in plumbing systems?

The purpose of a trap in plumbing systems is to retain a small amount of water which creates a seal that prevents sewer gases from entering the living spaces of a building. Traps are typically U-shaped sections of pipe that hold water at all times. This water barrier is crucial because it blocks harmful gases that can be produced in the sewer system, such as methane and hydrogen sulfide, from escaping into the interior of a home or building.

By allowing a small volume of water to remain in the trap, it effectively creates a physical barrier while still permitting wastewater to flow through the plumbing system. This function is essential not just for maintaining hygienic conditions but also for ensuring the proper operation of drainage systems.

If other options were under consideration, like creating water flow, this is not a function of traps; instead, they work in conjunction with the flow of wastewater. Similarly, traps do not increase water pressure; rather, they are passive components in the gravity-based drainage system. Finally, filtering debris from wastewater is not the primary function of a trap; other devices, such as grease interceptors or screens, are designed with that purpose in mind.