What is backsiphonage?

Backsiphonage is backflow caused by a negative pressure in a public water system or consumer’s potable water system. Negative pressure is also known as a vacuum or partial vacuum: in similar fashion to drinking water through a straw, backsiphonage can draw harmful contaminants and pollutants in one water system to flow out to another’s, to great negative result. Backsiphonage can occur when there is a stoppage of water supply due to nearby firefighting, a break in a water main, routine maintenance flushing, or any other situation that causes a significant loss in water system pressure. Figure 3 shows how a backsiphonage scenario can occur.Diagram, engineering drawing  Description automatically generated

Figure 3 – As firefighters combat the fire across the street, this depletes the water supply below. This reduces the pressure in the supply line below atmospheric pressure, creating a siphon that can draw pollutants and contaminants from the local water system to the greater water supply (Image Credit: AWWA)

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1. Why does the City of Petersburg Public Utilities Division have a Backflow Prevention & Cross Connection Control Program?
2. What is a cross-connection?
3. What is backflow?
4. What is backpressure?
5. What is backsiphonage?
6. Why is backflow a concern to the public?
7. Are all residential homes required to have backflow assemblies?
8. Why are irrigation systems considered to be hazardous to the water system?
9. What type of backflow prevention assemblies are allowed in irrigation systems?
10. How do I know if I have a backflow prevention assembly?
11. What kind of buildings need backflow prevention assemblies?
12. Is there a minimum height that the backflow assembly must be installed?
13. When is a plumbing permit required?
14. Can a backflow device be removed?
15. How frequently does a backflow prevention assembly have to be tested?
16. How much will the inspections/maintenance cost?
17. What credentials are required to inspect and test a backflow prevention assembly?
18. Will I receive notification when to perform my test?
19. What if I don’t receive a letter?
20. What can I do with my test report?
21. Abbreviations