Interpretation No. 6070 – Backflow Prevention and Cross-Connection Control

Manual Reference Section: 6
Applicable Code: BC Plumbing Code (1998), Part 7, Section 7.6
Status: Approved

Background

Interpretation No. 6070 represented one of the most detailed rulings produced by the Plumbing Officials’ Association of British Columbia. The enquiry arose from inconsistencies observed in the field regarding the selection and installation of backflow prevention assemblies on potable water supply systems. Inspectors from multiple jurisdictions had reported varying practices in how cross-connection hazards were being assessed and what grade of backflow preventer was being specified for different risk categories.

Subject Matter

The central question concerned the criteria for determining the appropriate degree of hazard at a given cross-connection point and, consequently, the correct type of backflow prevention assembly required under Subsection 7.6.2 of the 1998 BC Plumbing Code. Specific attention was given to the distinction between severe and moderate hazard classifications, as these designations dictated whether a reduced-pressure principle (RP) assembly or a double-check valve assembly (DCVA) was acceptable.

Ruling

The Association ruled that the degree of hazard must be evaluated at each point of cross-connection, taking into account both the nature of the substance that could enter the potable supply through backflow and the probability of such an occurrence. A severe hazard, as defined in the Code, exists wherever a substance that could cause illness or death might be introduced into the potable water system. In such cases, the installation of a reduced-pressure principle backflow prevention assembly conforming to CSA B64.4 was mandatory.

For moderate hazard conditions, where the contaminant would be objectionable but not a direct threat to health, a double-check valve assembly conforming to CSA B64.5 was deemed acceptable. The ruling clarified that aesthetic concerns such as taste, odour, or discolouration constituted moderate rather than severe hazards, provided that no toxic or pathogenic agents were present.

The interpretation further specified that all backflow prevention assemblies must be installed in an accessible location to facilitate the annual testing and maintenance required by the authority having jurisdiction. Assemblies installed in below-grade vaults were required to have adequate drainage provisions to prevent submersion, which could compromise the operation of the relief valve on RP devices. The reference standard for field testing procedures was CSA B64.10, and only certified testers were permitted to perform the required inspections.

Premises-isolation backflow preventers installed at the water service entry point did not eliminate the obligation to provide point-of-use protection at individual cross-connections within the building, where the degree of hazard warranted such measures.

Scope of Application

This interpretation applied to all building categories, including residential, commercial, industrial, and institutional occupancies. It supplemented but did not replace any municipal cross-connection control bylaws that imposed additional requirements beyond the provincial Code.

For a broader overview of cross-connection control requirements across BC municipalities, see Cross-Connection Control and Backflow Prevention in British Columbia