Cross-Connection Frequently Asked Questions


"Cross-connection" or "cross-connected" as used in these regulations means any real or potential connection between any part of a public water system or other water system supplying potable water to members of the public and any auxiliary water supply or any source or system containing water or any substance that is not or cannot be approved as safe, wholesome, and potable for human consumption.

Three things must happen in order for a backflow incident to occur:

  1. An actual or potential cross-connection,
  2. A non-potable water source is present,
  3. Backpressure or a vacuum created within the plumbing.

An actual cross-connection is a cross-connection that is subject to both back-siphonage and backpressure.

A potential cross-connection is cross-connection that is subject to only back-siphonage (example, a garden hose extending into a swimming pool).

Backflow prevention assemblies are testable U.S.C. approved devices that are designed to prevent water from flowing back into a public water system.

The backflow prevention assembly should be installed as close to water meter as possible, as approved by the County of San Luis Obispo Environmental Health Services Division. Generally, the assembly should be no further than ten (10) feet from the water meter.

A “Lead Free” reduced pressure principle (RP) style backflow prevention assembly is required on domestic water service lines. RP style backflow prevention assemblies are also required on irrigation water service lines but are exempt from the “Lead Free” requirement. A Double Check or Double Check Detector Assembly are only allowed on fire sprinkler systems.

Approved backflow prevention assemblies

Yes, if a Water Department, Water Purveyor or the County Cross Connection Program required a backflow prevention assembly be installed, then you are required to test it at least annually per San Luis Obispo County Code of Ordinances Title 8 Chapter 8.30

Yes, The Cross Connection Prevention Program will provide reminders forty five (45) days prior to the due date. Second due notices are sent out fifteen (15) days after the due date has elapsed. Final notice and recommendation that water services be terminated occurs thirty (30) days after the second notice has been mailed.

To request more information regarding your Backflow Prevention Assembly, have the service number of the assembly handy. The service number is a combination of the facility and device number and is represented by four numbers, a dash, then a three digit extension (example 9999-001) and is located in the upper right hand corner of the assembly test form.

Contact Matt Giuffrida at [email protected] or (805) 781-5567; or Carrie Zuur-Lopez at [email protected] or (805) 781-5544 to request information about your assembly.


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