The answer to 'how does backflow preventer work' is a backflow preventer is a mechanical device that prevents water from flowing backward into the potable water supply. It is designed to maintain the direction of water flow in a plumbing system, ensuring that contaminated or polluted water cannot flow back into the clean water supply.
Backflow preventers are typically installed at the point where the main water supply line enters a building, or at the connection point of any equipment or appliance that uses water. They contain a series of one-way valves that only allow water to flow in the intended direction, from the public water main into the home or building. If the pressure in the water main drops or a vacuum is created, the backflow preventer's valves will automatically close, preventing any potentially contaminated water from being drawn back into the clean water supply.