What is the purpose of a backflow preventer in an irrigation system, and where should it be installed?

• A. It stores excess water for drought; installed in landscape bed.
• B. It regulates water pressure; installed at irrigation controller.
• C. It prevents contaminated water from flowing back into the potable supply; installed at the water source or immediately downstream of it, following local code.
• D. It filters sediment from irrigation water; installed at main valve box.

Answer: (C)

The main idea is to protect the drinking water supply by preventing irrigation water from flowing back into it. A backflow preventer acts as a one-way barrier so that if pressure changes or a cross-connection creates a potential for reverse flow, contaminated irrigation water can’t siphon back into the potable line. This is why it must be placed at the water source or immediately downstream of it, and in compliance with local codes, so it sits right where the irrigation system connects to the public supply and can isolate the system from the main line. Regular testing and maintenance are typically required to ensure the device works correctly.

Other options don’t fit this purpose: storing water for drought, regulating pressure at the controller, or filtering sediment are different functions and don’t address preventing cross-connection backflow into the potable supply.