In plumbing, what is the primary purpose of a backflow preventer?

The primary purpose of a backflow preventer is to prevent contamination of the water supply. Backflow occurs when water flows in the opposite direction than intended, which can happen due to changes in pressure or back pressure in the plumbing system. This situation can lead to potentially hazardous materials, such as sewage or chemicals, being drawn back into clean water sources, posing significant health risks.

Backflow preventers are specifically designed to create a physical barrier that ensures the flow of water only moves in one direction—away from the potable water supply. These devices safeguard drinking water from contamination, ensuring that public health is protected and that water quality is maintained. Thus, the correct answer emphasizes the crucial role of backflow prevention in plumbing systems as a protective measure for the water supply.