Safe Drinking Water Program

Cross Connection and Backflow Prevention

THE BASICS

What is Backflow?

Water systems depend on water pressure to keep water flowing in the proper direction from the source through the pipes to your tap. However, anything that causes a drop in water pressure, such as a water main break or heavy use during a fire, can create a reverse flow from the customer’s plumbing system back into the public water system. This is called backflow.

Backflow can also occur when the customer’s water system has a higher pressure than the public water system. The water flowing backward could contain something that might contaminate the drinking water supply.

What is a Cross Connection?

A cross connection is a connection between drinking water (also known as potable water) and other water or fluids of unknown quality (also known as non-potable water).

To prevent against cross connection, backflow preventers are installed to stop the backflow of contaminated water into the drinkable water supply.

What Are Some Common Cross Connections?

Examples of common cross connections that require backflow protection: