What causes backflow?

If you are searching “What causes backflow?” you want a clear answer you can act on. Backflow can lead to dangerous, non-potable substances being introduced into public or private water systems, creating serious health and safety threats. 

Either back-siphonage or backpressure causes backflow. Back-siphonage happens when water pressure drops and creates suction that reverses flow. Backpressure happens when pressure in a non-potable system becomes greater than inlet pressure in a potable system, forcing water to reverse through a cross-connection.

The two causes of backflow

Back-siphonage

Back-siphonage is a sudden decrease in water pressure in the water distribution system. The reduction in pressure can create suction that reverses flow and pulls non-potable substances into potable water systems.

Backpressure

Backpressure is when the pressure in a non-potable system is greater than the inlet pressure of a potable system. Potable water may then be forced into a reversal of flow through the cross-connection, allowing non-potable substances to contaminate the potable water system.

Why the cause matters

Both causes can reverse water flow, but the conditions behind them are different. Understanding the cause helps property owners and facility teams understand why backflow prevention assemblies are required on systems with cross-connections and why verification through Backflow Testing is important.

How Backflow Testing helps reduce risk

If you have a backflow prevention assembly installed, Backflow Testing verifies performance and supports certification documentation. Backflow Prevention Services tests backflow prevention assemblies and provides certification documentation to the appropriate authorities on your behalf.

Testing schedules can vary by city. Some cities require yearly testing, while others can be three or five years. Residential schedules can also vary by application, such as every three years on irrigation and yearly on isolation assemblies.

If your site has a backflow prevention assembly, schedule Backflow Testing with Backflow Prevention Services. Testing helps confirm the assembly is operating correctly and supports compliance documentation based on local requirements.

FAQ 

What causes backflow in a water system?
Either back-siphonage or backpressure causes backflow.

Can a water main break cause backflow?
A pressure drop such as a water main break can cause back-siphonage, which can reverse flow.

What role does a cross-connection play?
A cross-connection creates a pathway between potable and non-potable water or substances, making contamination possible when flow reverses.

How do I know if my assembly is working correctly?
Backflow Testing verifies assembly performance and supports required documentation.

How often is Backflow Testing required in Michigan?
Testing schedules can vary by city. Some require yearly testing, while others can be three or five years. Residential schedules can vary by application.

“What causes backflow?” has a direct answer: either back-siphonage or backpressure causes backflow. Because backflow can introduce non-potable substances into potable water systems, Backflow Testing is an important step to verify your backflow prevention assembly is operating correctly and documented properly in Michigan. Contact Backflow Prevention Services today to get started.