Which backflow device fits which hazard in Mesa, and where does it go? City Code 8-1-4 and 8-1-5

Section 8-1-4 says that, in addition to the lists in 8-1-8 and 8-1-9, the Department may require protection "based on the degree of hazard," using three factors: health, non-health, and plumbing hazard within the customer's system. Its table shows what each assembly protects against:

The Department may approve an alternative assembly that holds a Certificate of Approval from the USC Foundation for Cross-Connection Control and Hydraulic Research or another certifying body unrelated to the manufacturer and accepted in the industry (B). An air gap may be used inside a customer system if it is unmodified and matches the definition in 8-1-1 (C).

Section 8-1-5 sets the install rules:

• Who pays (A). The customer, at their own expense, to the Mesa Building, Plumbing and Fire Code standards.
• Where (B). "At, or as close as possible to, the point of delivery," and always before the first branch line that splits the customer water system.
• How big (C). At least the cross-sectional diameter of the service connection, unless the Department approves otherwise in writing.

• Backsiphonage. Water pulled backward by low pressure in the supply.
• Backpressure. Pressure in the customer's system higher than the city's, pushing water back.
• Health hazard. A condition that could contaminate the water, versus a non-health hazard that could only pollute it.
• Point of delivery. Defined in 8-1-1 as the downstream end of the water meter, where the city-owned system ends. For an unmetered service such as a fire line, it is just downstream of the valve separating the city-owned part.

Anyone choosing an assembly in Mesa. It applies to service protection and, with 8-1-9, to devices at equipment. The table's "not listed" cells mean the code does not credit that assembly with that protection.

A restaurant. Its service qualifies for an RPA under 8-1-8. The plumber sets it at the meter, before any branch feeds the kitchen, and sizes it to match the service line.

A landscape line. A PVB works where only backsiphonage is a risk and the assembly can sit above the downstream piping. See the 8-1-8 use list.

The edge case. A contractor proposes a smaller RPA to save money on a 2 inch service. Section 8-1-5(C) says the assembly must be at least as large as the service unless the Department approves in writing.

1. 1Identify the hazard level and the kind of backflow risk for each connection.
2. 2Pick from the 8-1-4 table, or the assembly named for your use in 8-1-8 or 8-1-9.
3. 3Locate the service assembly at the point of delivery, ahead of the first branch.
4. 4Match its size to the service, or get written approval for a smaller one.
5. 5Show the make, model and size on the plans and have a recognized tester test it.

• "A DCVA is fine for anything that is not sewage." It is not listed for health hazards.
• "Put it wherever there is room." The rule is at the point of delivery and before the first branch.
• "Downsizing the device is a value engineering win." It needs written approval.
• "Any certified device works." The Department approves assemblies, and alternatives need an independent certificate.