What is the purpose of a backflow prevention device?

• A. To prevent contaminated water from flowing back into the clean water supply
• B. To maintain constant water temperature
• C. To filter the water
• D. To regulate pressure in the system

Answer: (B)

The main idea is to protect drinking water by stopping reverse flow. A backflow prevention device acts as a barrier so water cannot flow backward from non-potable sources (like irrigation, mop water, chemicals, or contaminated taps) into the clean water supply. When system pressure changes or a cross-connection creates a potential siphon, the device uses check valves or an air gap to allow water to flow only in the intended direction, preventing contamination of the potable water.

Other functions listed don’t fit this purpose. Maintaining constant water temperature is handled by temperature-control devices, not backflow preventers. Filtering removes particulates, which is a different function from stopping backflow. Regulating pressure is the job of pressure-reducing or -relieving valves, not preventing backward flow.