Backflow Prevention FAQs

1. Why does the City of Shafer MN  need a Cross-Connection and Backflow Testing Program?

  • The program safeguards the public drinking water and protects the health of its customers by ensuring that any contaminants that could backflow into the public water supply system are isolated within the customer’s internal distribution system.

2. What is backflow?

  • Backflow refers to the reverse flow of non-potable water, or other substances, through a cross-connection and into the piping of a public water system or customer’s potable water system. Two types of backflow are backpressure backflow and back-siphonage.

3. What is a backflow prevention assembly or device?

  • A backflow prevention assembly or device is a means or mechanism to prevent backflow. The most basic means for preventing backflow is an air gap, which either eliminates a cross-connection or provides barrier from backflow. A safer mechanism for preventing backflow is a mechanical backflow preventer, which provides a physical barrier to backflow. The principal types of backflow preventers are the reduced-pressure principle assembly (RP or RPZ), the pressure vacuum breaker assembly (PVB), the double check valve assembly (DC), and the spill-resistant pressure vacuum breaker assembly.

4. What is the process for installing/replacing a backflow prevention assembly?

  • Proper permits must be acquired from the Building Department; to contact their office, 651-257-4726. 

5. Why do backflow prevention assemblies need to be tested?

  • Mechanical backflow prevention assemblies have internal seals, springs, and moving parts that are subject to fouling, wear or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow prevention assemblies have to be tested periodically to ensure that they are functioning correctly. Mechanical backflow prevention assemblies have to be tested with properly calibrated gauge equipment.

6. How often does the backflow prevention assembly need to be tested?

  • To ensure the proper operation of a backflow prevention assembly, the assembly must be tested and certified upon installation and at least once a year thereafter by a licensed backflow tester/rebuilder.

7. How can I contact a licensed backflow assembly tester/rebuilder?

  • A list of licensed testers can be found at Under the Property Owner tab, select Backflow Tester Search for annual testing or Backflow Rebuilder Search if your device has failed inspection and needs to be rebuilt.

8. When requesting a test for my backflow prevention assembly, how much should I expect to pay for this service?

  • Fees typically range from $70 each for multiple locations for the same customer up to $200 for a single location.  It is recommended to shop around when you are trying to schedule a tester.  

9. What type of document needs to be returned to the city as proof that testing of the backflow prevention assembly was completed?

  • The licensed tester will input the backflow test data on The database will immediately show your device as compliant if the test was properly logged and the fee paid by the tester.  If the customer’s backflow testing report is not inputted into SWC Shafer MN
     database by the due date, then the SWC will mail a past due notice to the customer. The city has access to and monitors compliance.

10. How can I verify that testing of my backflow prevention assembly has/has not been completed?

  • Go to, under the Property Owner tab select Backflow Device Test Status, enter your property address and hit Submit to verify whether your test results have been submitted.

11. Does a lawn irrigation system require a backflow prevention assembly?

  • Yes. Section 608.16.5, of the International Plumbing Code and Section P2902.5.3 of the International Residential Code (connections to lawn irrigation systems), states that the potable water supply to lawn irrigation systems shall be protected against backflow by a pressure-type vacuum breaker, a double-check valve assembly or a reduced pressure principle backflow preventer – depending on the degree of the site hazard.

12. How long does a backflow prevention assembly last?

  • With proper maintenance and annual testing, backflow prevention assemblies have been known to last for many years.

13. What is considered a “potential hazard” to the potable water supply?

  •  A “potential hazard” is defined as any possibility of pollutants, contaminants, and system or plumbing hazards. For example, fire protection system, irrigation systems, gasoline refineries and stations, restaurants, hospitals, and manufacturers.

14. Has the City of Shafer MN
 process for permitting or overseeing the inspection of new, relocated or repaired backflow prevention changed?

  • Yes. the City of Shafer MN will obtain additional information on backflow installations as part of the permitting process to ensure new assemblies get into the SWC database.

15. What is backpressure backflow?

  • Backpressure backflow occurs when the downstream side of the piping system is greater than the supply pressure in a public system or customer’s potable water system. Backpressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure or a combination of both. Pumps can create increases in downstream pressure, temperature increases in boilers, etc. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during waterline flushing, firefighting, or breaks in the water mains.

16. What is back-siphonage?

  • Back-siphonage is backflow caused by negative pressure (i.e. vacuum or partial vacuum) in a public water system or customer’s potable water system. The effect is similar to drinking water through a straw. Back-siphonage can occur when there is a stoppage of water supply due to nearby firefighting, a break in a water main, etc.

17. What is a cross-connection?

  • A cross-connection is any temporary or permanent connection between a public water system or the customer’s potable water system and any source or system containing non-potable water or other substances.
  • Common cross-connections:
    • Private Wells – where the private well connection is connected to a service line receiving water from a public water supply. The untreated water could be pumped into the potable water supply which serves the home and the public water system.
    • Lawn sprinkler systems – where the stagnant/contaminated water from the sprinkler system could be drawn into the drinkable water supply for your home.





Useful Links

AWWA video on backflow prevention

List of backflow testers and rebuilders near you

City of Shafer MN Backflow Prevention Program






































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