What is the primary purpose of a backflow preventer in a domestic cold water system, and where is it typically located relative to the water meter?

• A. It is installed on the building side of the water meter or at a protected cross-connection near the point of entry, accessible for testing.
• B. It is installed directly inside the water meter casing.
• C. It is installed only downstream of all fixtures.
• D. It is installed on the street main before the meter.

Answer: (A)

Backflow preventers exist to stop contaminated water from flowing backward into the clean potable supply when pressure changes or a cross-connection occurs. The best placement is on the building side of the water meter (essentially at the point of entry to the building), so that all of the internal piping is protected and the device can be readily tested and maintained.

Putting it on the building side boundaries protects the public water main from any backflow coming from inside the building, and its location near the entry makes testing accessible, which is required to ensure it works correctly.

Why the other placements aren’t suitable: placing the device inside the meter casing makes testing and maintenance difficult; locating it downstream of all fixtures would not guard the supply if backflow occurs upstream of those fixtures; and placing it on the street main before the meter would leave the building’s internal piping unprotected from backflow.