Backflow Prevention: Matching the Device to the Hazard

Why This Matters

Backflow protection is where plumbing turns into public health. CPC 602.2 says no one may connect the domestic water supply to piping carrying water from another source, used water, or chemicals, unless a backflow prevention device approved for the potential hazard is provided and maintained. As the installer, you pick the device, set it at the right height, and leave it testable.

The Vocabulary (CPC Chapter 2)

• Backflow: water or other substances flowing into the potable distribution pipes from a source other than the intended source.
• Backsiphonage: used, contaminated, or polluted water flowing back into a supply pipe because the pressure in that pipe dropped below atmospheric. A water main break or heavy fire flow can cause it.
• Backpressure backflow: backflow caused by pressure higher than the supply pressure, from pumps, boilers, gravity, or other sources.
• Cross-connection: any connection or arrangement between the potable supply and a fixture, tank, receptor, equipment, or device through which nonpotable or contaminated water or other substances could enter the potable system.
• Pollution (low hazard): an impairment of water quality that does not create a public health hazard but adversely and unreasonably affects its aesthetic qualities.
• Contamination (high hazard): an impairment that creates an actual public health hazard through poisoning or the spread of disease by sewage, industrial fluids, or waste.
• Critical level: the mark on a backflow device or vacuum breaker that sets the minimum height above the flood-level rim at which it must be installed.

The CPC uses those two degrees of hazard, low and high. Some water purveyors and training courses use other labels, but Table 603.2 is organized by pollution (low hazard) and contamination (high hazard), each split into backsiphonage and backpressure.