Back Flow Prevention

Cross Connection

A cross connection is a connection between piping that distributes potable water and the piping that distributes other types of water or substances that are not safe to drink or may impact the taste or odor of non-potable water.

Typical Residential Cross-Connections

  • Hose Bibs
  • Jacuzzis
  • Lawn Irrigation
  • Swimming Pools
  • Toilet Ball-Cocks

Back Flow

Backflow takes place when water flows from your homes water pipes back into the City of Longview water system that supplies your neighbors with their drinking water. This can happen when the main distribution system loses pressure due to events such as line breaks or withdrawal of large amounts of water for fighting fires.


The City of Longview requires all new and existing backflow assemblies be tested annually by a State of Washington certified backflow assembly tester. You may find a current list of certified backflow testers in Cowlitz County and the surrounding areas here.

All backflow test reports must be completed on the City of Longview Backflow Preventer Inspection and Field Test Report Form. Reports may be emailed to or mailed to City of Longview, Attn: Backflow, PO Box 128, Longview, WA 98632.


If your internal system has fixtures or connections that are not protected, toxins can be drawn back into the main system. For example, think of a garden hose with a plant food applicator attached. If water is siphoned out of your system, it will take the plant food with it. This will enter our distribution system and could end up coming out of your neighbors tap, causing illness or even death.

Back Siphonage

Leaving a garden hose in standing water such as a pool or hot tub can also siphon that water back into the system. How can you prevent this? Education about backflow is the first step and careful attention to situations that could introduce unclean water back into the system is very important.

Back Pressure

It can be created when a source of pressure, such as a pump, creates pressure greater than the supplied from the distribution system.

Installation of backflow devices is your best protection from this homeowner liability.