Which statement correctly defines a backflow preventer and when it is required?

Which statement correctly defines a backflow preventer and when it is required?

• A. A device to regulate back pressure after a filter.
• B. A device to regulate back pressure after the mainline.
• C. A device to prevent irrigation water from flowing back into the potable supply.
• D. A device to prevent irrigation water from flowing back into the potable supply.

Answer: (D)

A backflow preventer is all about protecting the drinking water supply by stopping irrigation water from flowing backward into the potable system when pressure changes or a cross-connection exists. The best statement matches this purpose precisely: it describes a device that prevents irrigation water from entering the potable supply. It isn’t about regulating pressure after a filter or after the mainline—that’s a different type of device, not the function of a backflow preventer. Codes require backflow prevention in any setup where there could be a cross-connection or where irrigation may be exposed to contaminants (such as chemical injectors, fertilizers, or other non-potable sources). In those cases, installing the appropriate backflow preventer ensures the potable water remains protected even if pressure fluctuations occur.

A backflow preventer is all about protecting the drinking water supply by stopping irrigation water from flowing backward into the potable system when pressure changes or a cross-connection exists. The best statement matches this purpose precisely: it describes a device that prevents irrigation water from entering the potable supply. It isn’t about regulating pressure after a filter or after the mainline—that’s a different type of device, not the function of a backflow preventer. Codes require backflow prevention in any setup where there could be a cross-connection or where irrigation may be exposed to contaminants (such as chemical injectors, fertilizers, or other non-potable sources). In those cases, installing the appropriate backflow preventer ensures the potable water remains protected even if pressure fluctuations occur.