On most Valley commercial properties, the main backflow assembly sits above ground on your side of the water meter, often near the street or a front building corner. It's a bronze or brass valve body with a shutoff valve on each end and small test cocks on top. An RPZ also has a relief port underneath.
Where cities want the assembly to be
Valley cities place the main assembly on purpose, so it isn't hard to predict. Phoenix calls it "secondary" protection: an assembly that protects the city main from the whole building. It has to be "as close as practicable" to the point of service delivery (City Code 37-144). Where a meter is installed, Phoenix defines that point as the customer's side of the meter (City Code 37-1, quoted in TRT 00634). If a driveway or sidewalk is in the way, it goes at the nearest point past the obstacle, "but in no event beyond the first tap." Phoenix also accepts a spot behind the front yard setback line or just around a building corner.
Two more rules narrow the search:
- Not underground. Phoenix won't allow an RP or double check assembly "in a basement, meter box, pit, or vault," and a pressure vacuum breaker "must be installed above ground" (City Code 37-144).
- Reachable. Every assembly "must be accessible for testing and maintenance." Scottsdale adds "with proper clearances above the ground" (Revised Code 49-63). Watts installation drawings show 12 inches minimum and 30 inches maximum, measured from the flood level to the bottom of the assembly.
So you're looking for something above grade, low to the ground, close to the meter and easy to get to.
What each type looks like
All the testable types share a family look: a valve body in line with the pipe, usually bronze or brass on smaller sizes and iron on larger ones, a shutoff valve at each end and a few small test cocks poking out of the body, where the tester hooks up the gauge hoses.
| Type | How to spot it | Where you'll usually find it |
|---|---|---|
| Reduced pressure zone (RPZ or RP) | Two check valves in one long body, and a relief valve port on the bottom open to the air, set between the two checks | Main service line of higher-hazard businesses; boiler and cooling tower feeds inside |
| Double check (DC) | Two check valves in a row, no relief port. BAVCO: "two approved independently operating check valves" between shutoffs, with four test cocks | Main service line of lower-hazard buildings; Scottsdale requires one on Class 1 to 3 fire systems |
| Pressure vacuum breaker (PVB) | An upright valve with a check valve, an air inlet under a cap on top, two test cocks and two shutoffs | Irrigation lines, standing above the landscape |
| Spill-resistant vacuum breaker (SVB) | The spill-resistant version of a PVB | Irrigation, and indoor point-of-use equipment |
A PVB has to sit high. BAVCO says it "must be installed 12" above the highest point of use or piping" downstream, which is why you often see one standing well above the shrubs on a sloped lot.
Big buildings sometimes have two assemblies side by side. Scottsdale requires parallel assemblies when a customer "requires a continuous water supply," so one can stay on while the other is tested (Revised Code 49-63).
Assemblies inside the building
The one by the meter isn't always the only one. Cities also require point-of-use protection right at certain equipment. Mesa's code lists many of them: RP assemblies on boiler makeup lines, carbonated beverage dispensers, autoclaves, dental chairs and car wash equipment, among others (City Code 8-1-9). Mesa wants these indoor assemblies no more than 5 feet above the floor, though you may have to pull an access panel to reach one.
So in a restaurant, check the soda system. In a building with a boiler, check the makeup water line. In a dental office, look at the chair supply. Each testable assembly has its own serial number and its own yearly test.
### Clues from the kind of building you have
The building itself hints at what you'll find. Mesa's list of required assemblies is a good guide for the whole Valley, since most cities key the device to the same risks (City Code 8-1-8):
- One meter, many tenants. A commercial or industrial building where "one service connection supplies multiple tenants" needs an RP at the service. Look near the meter that feeds the whole center.
- Taller buildings. Buildings "greater than three stories or 34 feet in height from curb level" need an RP, and so do buildings with booster pumps or storage tanks.
- Shared fire and domestic service. A water service that feeds both fire and domestic lines needs an RP in Mesa.
- A meter that also waters the landscape. A "dual use" meter must have its landscape connection isolated with an RP or PVB, on top of any assembly at the main service. So expect two: one at the meter and one where the irrigation line splits off.
Phoenix's list works the same way. Its program guide names "multi-storied buildings having booster pumps or above ground storage tanks" among the uses that need an air gap, RP or double check.
### Fire sprinkler assemblies are separate
If the building has fire sprinklers, expect a separate assembly on the fire service, apart from the one on the domestic water line. Scottsdale's code sets the device by fire system class, a double check for Class 1 to 3 systems and an RP for Classes 4 to 6 (older Class 1 and 2 systems may keep a single check valve that is inspected yearly), and requires both service connections to carry protection for the higher hazard when both exist (Revised Code 49-62). In Phoenix, a backflow assembly on a fire line needs permits from both Planning and Development and the Fire Department (TRT 00634).
Leave fire line valves alone. Phoenix's test instructions tell testers to notify the alarm company that monitors the fire system, or the Fire Department, before testing one, because closing a valve on that line can affect fire protection for the building. Testing a fire line assembly is fire system work. In Phoenix, the tester must also be permitted by the City Fire Marshal (City Code 37-143).
The fastest way to find it: your paperwork
Phoenix's test report form asks for the water meter number, the assembly's serial number and the "on-site location of assembly." So last year's report tells you exactly where to look. If you don't have it, ask your water provider. Phoenix keeps an inventory of every required assembly, and most providers can tell you the location and type on file for your address.
Two quick tips while you're out there:
- Match the serial number. Find the serial number on the assembly body and compare it to the report, since the report is filed by serial number.
- Don't open the test cocks or turn the shutoffs. Closing a shutoff cuts water to the building. Testing is work for a certified tester.
If your assembly is spitting water, why an RPZ backflow preventer spits water explains what that means. To learn which type your business needs, see RPZ vs double check backflow preventers, and for irrigation valves, backflow preventers for sprinklers in Arizona.
HQ Plumbing & Air can locate, test and repair backflow assemblies on domestic water and irrigation lines, and repairs underground fire lines. HQ doesn't test or certify fire sprinkler systems or their backflow assemblies; that takes a fire-licensed contractor. Free estimates, upfront pricing.