Operator terms · Water
What is backflow prevention?
Backflow prevention is stopping used or contaminated water from flowing backward into the clean public supply. It uses devices such as air gaps, vacuum breakers, and backflow assemblies at cross-connections, and it is a core part of protecting drinking water in the distribution system.
Last reviewed 2026-08-03
Why backflow happens
If pressure drops in the main, water can be siphoned backward from a customer's plumbing into the public supply. A cross-connection, any point where the drinking water touches a non-potable source, is where that contamination can enter.
How it is prevented
The simplest protection is an air gap, a physical space between the water outlet and any surface. Where that is not possible, vacuum breakers and backflow prevention assemblies are installed and tested to match the level of hazard.
Common questions
- What is a cross-connection?
- Any point where the drinking water supply can meet a non-potable source.
- What is the simplest backflow protection?
- An air gap, a physical space that water cannot flow back across.
- Why does it matter?
- It keeps contamination from entering and spreading through the public water supply.