Cross Connections and Backflow Prevention

What is a Cross Connection?

A cross connection is a point in a plumbing system where the drinking water supply is connected to a non-potable source, like an irrigation system or other equipment. Pollutants or contaminants can enter the safe drinking water system through uncontrolled cross connections when a backflow occurs.

What is Backflow?

Backflow is the unwanted flow of non-potable substances back into the customer’s plumbing system and/or our public water system (i.e., drinking water). This backflow can occur when there’s a sudden difference in water pressure between the two systems during waterline breaks, repairs, or a water supply shut off.

Backflow preventers are mechanical devices designed to prevent backflow through these cross connections. However, for backflow preventers to protect as designed, they must meet stringent installation requirements and be inspected every year to ensure they’re working properly and preventing contamination from entering the drinking water. 

Washington State Requires Annual Backflow Inspection 

In our complex water system, everything is connected. The District's cross connection and backflow prevention program required by Washington State regulations is designed to keep pollutants and contaminants from entering your clean drinking water system. For example, if you have irrigation, fire sprinkler or other water using systems, you may need to have the connection between your systems and the District’s checked every year. It is important to ensure your backflow assembly valves are working properly to prevent pollutants and contaminants from entering the drinking water system. The District is committed to providing our customers clean, safe, drinking water. This is where we need you to do your part. 
Please take the reminder for your Annual Backflow Inspection seriously and schedule an inspection right away. Here’s a list of Backflow inspection vendors: 
Backflow Assembly Tester Convenience List

Everything is Connected and Needs Protection 

If you received a reminder letter that it’s time for your annual Backflow Prevention Inspection, this information will tell you what it is and why it’s important that you stay current on this inspection. Our clean drinking water depends on it. 


Want to Learn More About Cross Connections and Backflow Prevention?


District Standards 


Brochures and Related Information