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Backflow Overview

The Safe Water Drinking Act of 1974 requires the District to evaluate every residential and commercial connection served by our system.   The District passed Resolution #547 to establish and maintain a Cross Connection Control Program. The goal of the program is to prevent non-potable water from returning into the public water system.

What is Cross Connection and Backflow?

A cross connection is any connection to the public water supply that has the potential to backflow. Backflow is the reversal of flow from the intended direction

Is it important to prevent Backflow?

Washington Administration Code 246-290-490 requires all public water systems in Washington State to operate an on-going Cross Connection Control Program to protect the public water supply from contamination from possible cross connections.


Water District #20 strongly believes in having an active CCC program. The most effective method for the Water District to meet this requirement is to require customers to install a backflow prevention assembly on the main supply line to their property or facility, thus protecting the public water system from any cross connections that may be present inside a customer's plumbing system. All water users benefit from an active, on-going cross connection control program that includes the installation of backflow prevention assemblies.


The District evaluates backflow requirements for all commercial and residential buildings on an individual basis. Buildings that present an actual or potential backflow hazard are required to install a backflow prevention assembly that is appropriate for the degree of hazard (risk).


The District determines the backflow hazard by having a qualified CCC Specialist conduct a sanitation survey. This survey evaluates the type and purpose of the building, by what equipment and appliances the water is being used for and/or what product is being produced with the water. Certain types of buildings are mandated to have a backflow prevention assembly installed on their service line.  These buildings fall under Table 9 of the WAC 246-290-490.  Examples of these buildings include, but are not limited to:


  • Car Wash

  • Commercial Laundries or Cleaners

  • Food Processing Plants

  • Hospitals, Medical Centers, Nursing Homes, Veterinary, Medical and Dental Clinics, and Blood Plasma Centers.

  • Laboratories

  • Metal Plating Facilities

  • Piers and Docks

  • Wastewater Lift Stations and Pumping Stations

  • Survey Access Denied or Restricted Buildings


Questions contact us


Why does the customer have to pay for the installation of a backflow preventer?

The backflow preventer is installed to protect the public water supply against any hazard (actual or potential) in the customer’s water system. The actual or potential cross connection belongs to the property owner and not to the District.  Once water leaves the meter the water could be altered and the District does not want the water back nor do our customers. If a backflow assembly is required, the person who created the risk shall purchase, install, maintain and annually test the backflow assembly.

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