What is backflow? Backflow occurs when hydraulic conditions within our water distribution system deviate from “normal” and flow reverses, causing pollutants and contaminants to enter the system.

What causes backflow? Backflow is possible in two situations: backsiphonage and backpressure.

What is backsiphonage? When the pressure in the water distribution system drops suddenly (for example, during firefighting or a water main break), flow can reverse. This can create a suction effect, drawing the nonpotable substance into the water system.

What is backpressure? Backpressure is created when the pressure in a nonpotable system — such as a recirculating system containing soap, acid, or antifreeze — exceeds that in the potable system that provides make-up water. This can force the potable water to reverse its flow direction through the cross connection. Nonpotable substances can then enter the potable water system.

How can backflow be prevented? Flagstaff recognizes four methods of backflow prevention: air gap, reduced-pressure principal backflow prevention assembly, pressure vacuum breaker assembly or spill-proof vacuum breaker, and double-check backflow prevention assembly. The Industrial Pretreatment Program will determine which type is required based on the degree of hazard your property represents to the potable water supply.

What is a backflow assembly? A backflow preventer is an approved, testable assembly that uses valves, in different configurations, to prevent polluted or contaminated water from reversing direction and flowing backward.

How is an assembly approved? It goes through an approval process at the Foundation for Hydraulic Research and Cross Connection Control at the University of Southern California. This two-step process consists of laboratory tests and 12 months of field testing. Assemblies successfully completing the entire testing procedure are recognized by the City as approved.

Who is required to have a backflow prevention assembly? Backflow assemblies are required for commercial and industrial customers, as well as for residences where nonpotable water (such as reclaimed water) is used on site. State regulations exempt single-family residences used solely for residential purposes if there are no hazards present. The City’s Industrial Pretreatment Program decides whether backflow assemblies are required on a case-by-case basis. New facilities must install assemblies in a hot box outside of the building (unless it is for the fire riser — then it can go in the fire riser room with adequate drainage to the sanitary sewer), as close to the water meter as possible. Copies of City Ordinance #7-03-001-0015 and State Administrative Code rule R18-4-215 are available in the City Clerk’s office or from the Industrial Pretreatment Program at (928) 213-2117.

How do I know if I need a backflow prevention assembly? You will receive a notifying you of the need for a backflow prevention assembly. Staff from the City’s Industrial Pretreatment Program will evaluate your property. You will be informed of the City’s decision upon completion of the inspection or review of your plans.

Is there a general compliance schedule and process? Yes. Unless you make other arrangements with Industrial Pretreatment Program, the backflow prevention assembly must be in compliance within 30 days from the date of the initial notification. You will receive a follow-up notice after 30 days. After 45 days, you will receive a notice informing you that your water service may be discontinued unless you achieve compliance. If at any time during this process you have a problem meeting this schedule, it is extremely important that you contact the Industrial Pretreatment Program immediately, at (928) 213-2117, to make special arrangements for an extension.

Who can install a backflow prevention assembly? The customer is responsible for installing the backflow prevention assembly. It may be installed by a property owner, plumbing contractor, or a general contractor, subject to the Rules and Statutes of the Arizona Registrar of Contractors. Permits are required to install or replace these assemblies. Permits are issued by Flagstaff's Building Safety Department. Please call (928) 213-2618 for additional information.

Where should a backflow prevention assembly be located? The assembly must be located as close as possible to the water service connection but must remain on private property. Contact our Industrial Pretreatment Program at (928) 213-2117 for information on variances.

Who is responsible for testing and maintaining the backflow assembly? It is the sole responsibility of the customer to ensure that the assembly is in satisfactory operating condition at all times. Notices will be sent advising customers when an annual test is required so they can contact a recognized backflow assembly tester. If any repair work or maintenance is performed on the assembly, a recognized tester must retest the assembly immediately and submit the results. Contact Jolene Hayes at (928) 213-2117 for instruction on how to submit the backflow prevention assembly test result.

I have multiple testing dates for the backflows at my property. Can I consolidate the dates? Yes, a customer may request a change of the annual test compliance date for any assembly. No compliance date may be changed to be more than 12 months after the most recent test. Please contact Industrial Pretreatment at (928) 213-2177 or pretreatment@flagstaffaz.gov. 

BSI Online
List of Approved Assemblies