Cross Connection Control General Information

A cross connection is an actual or potential physical connection between our drinking water and anything that could pollute or contaminate the water supply. For example, food and beverage processing equipment without backflow preventers, have the potential for chemicals and/or contaminants to flow back into the system and contaminate the water supply.


Backflow is the undesirable reversal of flow of non-potable water or other contaminants through a cross connection and into the water distribution system. When the flow is reversed or "backflow" occurs, contaminated water can flow backward, drawing a contaminant into the water supply. There are two types of backflow - backpressure and back siphonage.

Back Siphonage Graphic

Backflow is typically caused when an unforeseen change in water pressure allows the water to flow in reverse of the normal direction in the water distribution system, creating the potential for a contamination to a drinking water supply. A drop in pressure could be caused by a variety of circumstances, including a water main break or the need to fight a fire.

To prevent backflow contamination, the City of Bainbridge Island follows cross-connection control requirements of the Washington State Department of Health. Installation of specific backflow protection assemblies and annual testing are required per the adopted Washington Administrative Code.

Possible Cross-Connection Locations

Some situations that can result in cross-connection issues include:

  • Irrigation or lawn sprinkler equipment
  • Food and beverage equipment
  • Wash basins and service sinks
  • Laboratory equipment
  • Fire sprinkler systems
  • Chemical feed equipment
  • Boilers
  • Radiant Heat

More Information

For answers to specific cross-connection control questions, please contact the cross connection control specialists at Operations and Maintenance by email or phone (206.842.1212).