A backflow preventer (BFP) is typically used to protect what?

A backflow preventer (BFP) is designed primarily to protect the public water supply from contamination or pollution caused by backflow. Backflow can occur when there is a sudden change in pressure in the water supply system, which can cause water from a potentially contaminated source to flow back into the clean water supply. The backflow preventer functions as a physical barrier, ensuring that water flows only in the intended direction and thereby safeguarding the health of the public and the integrity of the overall water system.

While it can contribute to protecting the internal plumbing system by preventing contaminated water from entering, its primary role is to maintain the safety of the public water supply. Other options, like the drainage system and the building's structural integrity, do not align with the purpose of a backflow preventer. The focus is specifically on preventing contaminants from entering the public water supply, making it crucial for public health and safety.