Gilbert Town Code 10-92(c): which backflow assembly does your kind of property need?

The rule. Subsection (a) requires a backflow prevention assembly approved by the department on each water service line to a customer's water system, except single-family residences exempt under the state administrative code, section R18-4-115(C), which the state has since renumbered R18-4-215. For new service, the assembly goes in before a certificate of occupancy is issued for the structure.

The conditions. Subsection (b) adds when one is required regardless of type: premises with an auxiliary water system, premises with substances that can create a health hazard to the public supply, internal cross connections the officer judges not correctable, premises where a full cross connection survey is impossible or impractical, and premises with a repeated history of cross connections.

The list. Subsection (c) sets the types for facilities "including but not limited to" a list of 40 entries, "unless the officer determines an alternate type of protection is either required or adequate to protect the public water supply or that no actual or potential hazard to the public water supply system exists."

• RP (reduced pressure) assembly: two check valves with a relief valve between them. The strongest testable assembly.
• DC (double check) assembly: two check valves. Used where the hazard is lower.
• AG (air gap): a physical gap between the outlet and the water level. Listed as an alternative for water trucks and hydrant connections.
• Officer: the town's backflow officer, who can require a different type than the list shows.

Nearly every commercial, industrial and institutional customer. Single-family homes that state rules exempt are the only carve-out in (a). The list itself names the facility types, and the catch-all entry, "any premises where a cross connection is maintained", is RP.

A dental office in a strip center. Item (22) lists medical and dental buildings as DC. That is the minimum type. The officer can still require a stronger assembly if the plumbing calls for it.

A four-story office. Over three stories or 34 feet from curb level gets a DC. If the building also has house pumps or a storage tank, item (8) lists DC for that too.

The edge case: a restaurant. Gilbert's list does not name restaurants, and food processing plants are DC. A restaurant is not automatically exempt: the catch-all and subsection (b) apply where there is a cross connection or a health hazard, and the officer can require a type. Ask the backflow program before you finalize the plans.

1. 1Find your property type in the list. If it is not there, ask the backflow program which type the officer expects.
2. 2Put the assembly on the plans for a new service and get it approved by the department.
3. 3Plan for the assembly to be in, and inspected, before the certificate of occupancy.
4. 4Hire a Town-recognized tester (the Backflow Prevention Department keeps the list) for the first test and the annual tests that follow. Gilbert's backflow program is on the town's website and at 480-503-6826.
5. 5If you add a booster pump, tank, irrigation system or auxiliary water source later, recheck the list.

• "RP and DC are interchangeable." The list names the type for each property, and the officer can require a different one.
• "If it is not on the list, I am exempt." The list says "including but not limited to", and the catch-all covers any cross connection.
• "Every Valley city lists the same properties." Tempe puts laundries and medical and dental buildings at RP where Gilbert lists DC, and Mesa and Scottsdale name restaurants where Gilbert does not.
• "A dental office is low hazard, so nothing is needed." It is on the list as DC.