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Cross Connection Control Program

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It’s Redwood City’s responsibility to protect the public drinking water supply from contamination that might occur through unintentional “backflow.” That’s the undesirable reversal of flow in a drinking water distribution system which may introduce objectionable substances into the drinking water line.

Backflow: The undesirable reverse flow of non-drinking water back into a drinking water system

A backflow situation could occur if the drinking water system suddenly loses pressure. For example, if large quantities of water were being pulled from the system to fight a fire, or there was pipeline break with the loss of significant amounts of water.

Cross Connection: The point at which a non-drinking water substance can possibly come in contact with drinking water; for example, when a drinking water line comes from the same source as a sprinkler system, hot tub, ornamental pond, or fire sprinkler system.

If backflow conditions were to occur, then our water could become contaminated through “cross connections.” A cross connection is a connection or potential connection between the City’s drinking water system and any other system or environment that may contain harmful or objectionable substances that could possibly enter the drinking water system. Cross connections are necessary – for example, a drinking water line likely comes from the same source as a home’s sprinkler system, hot tub or pool line, or ornamental pond. Wherever there is a cross connection, there must be a device called a backflow prevention assembly. This device prevents the undesirable reversal of water flow into the drinking water line.

How would a backflow preventer keep drinking water safe?

Backflow Prevention Assembly: A device installed in a water system which prevents the reverse flow of non-drinking water back into a drinking water line.

An example is a home or business fire sprinkler system. Such a system gets its water from the same source as that building’s drinking water. However, water can sit in the fire sprinkler line, become stale and sour, and be unfit for drinking. A backflow prevention assembly in this example has a valve which only allows water to move in one direction, so it will prevent that stale water in the sprinkler lines from reversing and getting into the drinking water line. The same goes for landscape irrigation pipelines for a home or business, or an industrial site that uses chemicals and water.

2 Inch ShortHarmful or objectionable substances may be gases, liquids, or solids such as chemicals, waste products, contents of auxiliary water systems (like groundwater wells, industrial fluids, and recycled water), or another substance that may change the color, add odor, or in any way change the quality of the drinking water.

Protecting the City’s drinking water supply can only be achieved by implementing an effective Cross Connection Control Program to identify sites at possible risk for harmful backflow, and by periodically inspecting and evaluating backflow prevention assemblies.

Cross Connection Control Program: A City program which identifies sites with possible backflow risk, and requires inspection and evaluation of backflow prevention devices.

Redwood City’s Cross Connection Control Program consists of routine inspections to determine the degree of risk for backflow that may exist at various sites. The degree of risk will determine the type and location of a required backflow prevention assembly.

8 Inch ShortTo accomplish this, the City’s Cross Connection Control Ordinance requires that annual tests and inspections be performed on all backflow prevention assemblies. To ensure that these required tests and inspections are completed, the City sends an annual notice to backflow assembly users notifying them when the test is due for their site. Backflow assembly tests can only be performed by professionals who have been certified by the City and who are on the City’s approved Backflow Prevention Assembly Tester List.

Certified backflow assembly testers are required to use the City’s Backflow Prevention Assembly Field Testing and Maintenance Report when annual tests are completed.

Official test forms are available at the following locations:

Public Works Department
1400 Broadway Avenue
Redwood City, CA 94063

   or    City Hall
1017 Middlefield Road
Redwood City, CA 94063

Completed test forms must be returned to the Public Works Department within thirty days following the testing due date. Incomplete forms will result in a “failed” test and a repeat test will be required.

The processes required in the Cross Connection Control Ordinance are important in ensuring that the community’s drinking water remains safe and of high quality.


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