What does a backwater valve prevent in a plumbing system?

A backwater valve is specifically designed to prevent sewage and wastewater from backing up into a property through the sewer lines. It functions as a one-way barrier, allowing sewage to exit during normal conditions but closing off if the sewer line becomes overwhelmed, such as during heavy rain or flooding. This is critical for maintaining sanitary conditions within a building and preventing potential health hazards that could arise from sewage spilling into living spaces.

While the other options pertain to issues that may occur in plumbing systems, they are not directly related to the primary function of a backwater valve. For instance, odor intrusion and water contamination address other aspects of plumbing that do not involve backflow prevention, while pest invasion pertains to structural integrity and hygiene rather than sewage management. Thus, the primary and correct role of a backwater valve is to guard against sewage backup.