What makes a backsiphonage event occur?

• A. Downstream pressure exceeds supply pressure, such as from a boiler, elevated storage tank, booster pump, or thermal expansion in a closed system.
• B. Backpressure causes a reverse flow.
• C. An air gap within the system prevents flow.
• D. Containment is always ineffective.

Answer: (A)

Backsiphonage occurs when the pressure on the downstream side becomes higher than the pressure in the supply line, creating a path for water to be drawn backward through a cross-connection. When equipment like a boiler, an elevated storage tank, a booster pump, or thermal expansion in a closed system raises downstream pressure, it can push water back toward the source through any cross-connection, pulling potential contaminants with it. An air gap actually prevents flow and stops backflow, so it wouldn’t cause backsiphonage. Proper containment can be effective if properly designed and used with backflow prevention devices.