Which device is used to prevent backflow contamination from entering the public water supply?

• A. Check valve
• B. Gate valve
• C. Butterfly valve
• D. Gate box

Answer: (A)

Preventing backflow into the public water supply relies on a device that automatically stops water from moving in the reverse direction when pressure changes. A check valve is designed for this purpose: it allows flow in one direction and closes automatically when downstream pressure tries to push water back upstream, preventing contamination from entering the supply. Gate valves and butterfly valves are mainly used to start, stop, or regulate flow; they do not inherently stop reverse flow and can still permit backflow under some conditions. A gate box is simply an access point for a buried valve and has no backflow prevention function. In practice, protecting the potable water system from cross-connections typically involves a check valve or other dedicated backflow preventer, especially in higher-risk scenarios.