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Backflow and Cross Connection

Backflow is the plumbing term for an unwanted flow of water in the reverse direction.

When you connect to the City of Ridgefield water distribution center, the intention is for the water to flow from the system to the customer. However, the flow of water could be reversed from the customer back into the distribution system. If cross-connections exist within the customer’s plumbing system when this backflow occurs, then it is possible to contaminate the public water supply.

There are two types of backflow — backpressure backflow and backsiphonage.

Backpressure backflow occurs when the pressure of the nonpotable system exceeds the positive pressure in the water distribution lines; that is, the water pressure within an establishment’s plumbing system exceeds that of the water distribution system. For example, the pressure in a hot water boiler system increases to a point that it exceeds the pressure in the water distribution system, a backflow from the boiler to the public water system may occur.

Backpressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure or a combination of both. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during water line flushing, fire fighting or breaks in water mains.

Backsiphonage occurs when there is a partial vacuum (negative pressure) in a water supply system, which draws the water from a contaminated source into a potable water supply. The effect is similar to siphoning or drinking water through a straw.

For example, during a large fire, high flows of water are pumped out of the distribution system through a fire hydrant. This can result in significantly reduced water pressure around the withdrawal point and create a partial vacuum in the system, causing suction of contaminated water into the potable water system. During such conditions, it is possible for water to be withdrawn from nonpotable sources located near the fire hydrant. Air-conditioning systems, water tanks, boilers, fertilizer tanks and washing machines are possible sources of backsiphonage. 

Backflow Prevention Devices

A backflow preventer is a method or mechanical device to prevent backflow and provides a physical barrier to backflow.

Required Annual Testing of Backflow Prevention Devices

The City of Ridgefield’s Cross Connection Control Program requires any customer who has a backflow prevention device to test their backflow assemblies:

  • After initial installation
  • After any repair, replacement or relocation
  • Annually by a certified backflow assembly tester

Annual inspection of Backflow prevention devices is mandated by RMC 13.55.040.

As a courtesy, our Public Works Department sends reminder letters when it is time to have your backflow assembly tested.  

The city’s letter notification cycle is April through September. Annual testing is required per the Department of Health WAC 246-290-490(5)iv. If you recently built a house and have a backflow assembly on your premises, the next test will become due between April and September of the following year.

You can find a current list of City Approved and Certified Backflow Testers at the top of this page. Please note, this list is provided as a convenience only and is not intended to endorse or recommend a particular service.


A cross-connection is any temporary or permanent connection between a public water system or consumer’s potable (i.e., drinking) water system and any source or system containing non-potable water or other substances.

Examples of Common Cross Connections

  • Hot tubs
  • Auxiliary water systems (wells)
  • Hoses submerged in polluted or contaminated water
  • Water (from a well or pond) pumped into an irrigation system directly connected to the water supply system
  • An underground lawn sprinkler system directly connected to the water supply system
  • A fountain or swimming pool directly connected to the water supply system for filling

Washington State Law WAC 246-290-490 City of Ridgefield Ordinance RMC 13.55.010

Irrigation Systems

If you have or are planning on installing an irrigation system, you must first comply with state and local laws. These laws require that all irrigation systems have approved backflow protection. A plumbing permit is also required when installing an irrigation system. Without proper backflow protection, your irrigation system could endanger the health of your family, neighbors, and others in the community who are using the public water supply system.

Web Test Entry for Backflow Testers

Testers are required to enter their test reports in our web test portal. Usernames and passwords have been provided by the City. If you have forgotten your login credentials click here to send an email to the City requesting your username and password.

For more information on the Web Test Portal please see the “Related Documents” below.

For more information regarding cross connection please contact the City’s Cross Connection Coordinator at 360-857-5010.

A New Way to Submit Tests

  1. Test the backflow assembly
  2. Log into the Web Test Portal
  3. Enter the serial number and the house number to locate the backflow assembly
  4. Enter test results (on a simple test entry screen)
  5. Enter suggested changes, e.g. model, size, serial number (if appropriate)
  6. Click submit and pay the fee
  7. Print a completed test report for the customer (optional)

Redefine the Paperwork

Enter test results in the field using a tablet with a WiFi connection or a smartphone. Upload them in the field or wait until you are back in the office, or continue using paper in the field and submit them online when you are back in the office.

The website will track your submitted tests; you will no longer have to contact the utility to find out if your tests have been received. The website confirmation number is all you need to confirm the tests have been uploaded to the utility.

Frequently Asked Questions

Why is backflow prevention important?
Backflow into a public water system can pollute or contaminate the potable water in that system (i.e., backflow into a public water system can make the water in that system unusable or unsafe to drink). Water suppliers and consumers have a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances.

I received a letter saying I need to install a backflow preventer. How do I do that?
The City of Ridgefield Public Works Department recommends contacting a licensed plumber.

I am a renter. Why did I receive a letter about the backflow preventer?
If you are renting a home or commercial space, your landlord or property management company would be responsible for obtaining a test.

I received a letter to test my backflow preventer at a home/property I sold previously. How do I update my information?
First, notify the Cross-Connection Program Coordinator, Lisa Blake, at 360.857.5010. Then, contact Utility Services to ensure your utility billing account is updated at 360.887.3557.

Why do backflow preventers have to be tested each year?
Backflow prevention assemblies have internal seals, springs, and moving parts that are susceptible to wear and failure. Yearly testing ensures they are functioning properly and protecting the public water system. It is required to protect the public water supply per WAC 246-290-490 and RMC 13.55.010.

Is there a general compliance schedule and process?
Generally, about 45 days prior to the test due date, the Public Works Department sends letters to all customers who are required to test their backflow assembly devices.

Do backflow testers work for the City of Ridgefield?
No. Backflow testers are independent private contractors. The City of Ridgefield does not install or test backflow assemblies. The State of Washington requires backflow tests to be performed by Certified Backflow Testers.

Review a list of City Approved and Certified Backflow Testers linked at the top of this page. This list is updated each year and requires testers to provide current year certifications. Tests performed and submitted by someone not on the city’s approved and certified backflow testers list will be rejected and considered invalid until that vendor provides the city with their current year state/city approved credentials.

How do I know if I need to install a backflow preventer?
Residential customers are only required to install a backflow preventer if there is a potential cross-connection hazard. It is the customer’s responsibility to notify us if an irrigation system or pool is installed. Backflow requirements vary for commercial/industrial customers based on the business’s water use. Ridgefield’s staff reviews newly established commercial/industrial water accounts to assess the degree of backflow hazard and notifies businesses about backflow requirements.

I don’t use my irrigation system.  Do I still have to test and maintain my backflow preventer?
As long as the irrigation system is connected to your plumbing system, the potential for backflow exists, and you must comply with all backflow requirements, including having it tested each year.

To eliminate these backflow requirements, the irrigation system must be physically disconnected and removed from your plumbing system. Contact a certified backflow tester to schedule the removal and notification to the Cross-Connection Coordinator (360) 857-5010. Public Works will schedule an inspection to confirm the backflow assembly has been removed and capped off.

If you have additional questions, please contact Lisa Blake, Cross-Connection Program Coordinator at or (360) 857-5010.

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