The answer to 'what causes backflow preventer' is that a backflow preventer is a plumbing device installed to prevent the reverse flow of water or other liquids into the clean water supply. This can happen when there is a sudden drop in water pressure, creating a vacuum that can suck contaminated water back into the clean water pipes. Backflow preventers are required by plumbing codes to protect public water systems from potential contamination.
Backflow preventers are commonly installed at the water meter, irrigation systems, and other locations where there is a risk of contamination. They work by using a series of check valves that only allow water to flow in one direction, preventing it from flowing back into the clean water supply.