In an ideal world, water would flow only from the public water system into customer homes and businesses. The reality, however, is that, under the right conditions, water that has made its way into customer plumbing systems can return to the public water system. When this flow reversal occurs, it is referred to as backflow.

There are (2) hydraulic conditions that can cause backflow:

1. Backpressure: Occurs when water pressure in the customer plumbing system exceeds the public water system pressure.
2. Backsiphonage: Occurs when the pressure in the public water system suddenly decreases. Pressure can suddenly drop during a firefighting event, a broken water main, or other high water demands by end users.

Cross-connections are a public health concern because any water reintroduced into the public water system can potentially carry contaminants with it. In this way, cross-connections can compromise the quality of the public water supply.

Backflow prevention assemblies, installed downstream of the water meter, offer GSWC a mechanism for ensuring contaminated water does not flow back into the public water system. They act as check valves that allow water to flow only in one direction; from the public water system into homes and businesses.

Not all backflow assemblies are created equal, with some offering higher protection than others. If GSWC requires installing a backflow assembly, the water user will be provided with a letter indicating the type of backflow prevention assembly/method that needs to be installed/implemented.

This backflow prevention assembly contains a check valve and an independently operating loaded air inlet valve. It is designed to protect against non-health hazards and health hazards under backsiphonage hydraulic conditions only.

This backflow prevention assembly has two independently acting check valves in series. It is designed to protect against non-health hazards under a backpressure or back-siphonage hydraulic condition.

A Double Check (DC) assembly, with an approved bypass line. The bypass line is equipped with a DC assembly and a water meter. The meter is included to detect leaks and unauthorized taps in the customer plumbing system. This backflow prevention assembly type is commonly used in fire protection systems posing a non-health hazard to the public water supply.

This backflow prevention assembly contains two check valves and a differential relief valve. It is designed to protect against non-health and health hazards under backpressure and back-siphonage hydraulic conditions.

A Reduce Pressure Principle (RP) assembly, with an approved bypass line. The bypass line is also equipped with an RP assembly and a water meter. The meter is included to detects leaks and unauthorized taps in the customer’s plumbing system. This backflow prevention assembly type is commonly used in fire protection systems posing a health hazard to the public water supply.

The most effective form of backflow prevention is the air gap—a physical separation between a water supply outlet and the highest potential water level in a receiving vessel. The air gap eliminates the possibility of backflow due to the absence of a direct connection to the piping. The physical separation is a vertical distance specified by regulations.

The hose bib vacuum breaker is a special application of an atmospheric vacuum breaker. These devices are inexpensive, easy to install, and provide a basic level of backflow prevention against backsiphonage hydraulic conditions only. GSWC advises installing these devices on every fixture where a hose connection can be made on your premise. Installation and operation guidelines for the hose bib vacuum breaker can be found in the California Plumbing Code.

State regulations require certain premises and business types to install backflow assemblies.  For those not explicitly required, a hazard assessment is conducted to determine if a backflow assembly is necessary to safeguard the public water supply from potential or actual contamination.

Backflow prevention assemblies, such as reduced pressure principle or double-check backflow prevention assemblies, are crucial safeguards against water contamination. They prevent unwanted backflow, reducing the risk of potential harm to the water supply. Golden State Water Company has adopted standard specifications for installing backflow prevention assemblies.

Golden State Water Company cannot recommend testers, nor do we maintain a list of certified testers. If you need a tester:

• Consult with your current plumber or contractor. These professionals usually hold backflow tester certification or know someone who can test your assembly.
• PLEASE NOTE: Whomever you select to test your BFA must be certified to do so. You should confirm that the plumber or contractor you select as a tester is certified. Testers must hold a current certification from the county, the American Backflow Prevention Association (ABPA), or the American Water Works Association (AWWA). Don’t hesitate to contact us if you are uncertain if your tester’s certification is acceptable.
• Search online using keywords such as “Backflow”, “Testers”, “Cross-Connection”, etc.
• Check your assembly. In some cases, the existing BFA has been tested before and would have a tag from the previous tester that shows the tester/ testing company’s phone number.

The backflow tester should use the annual test form supplied by Golden State Water Company, since it is pre-populated with unique identification numbers. If it is not available, the tester may use this approved blank form.

EPA Cross Connection Control Manual
Rule 16: Service Connections, Meters, and Customer’s Facilities
Division of Drinking Water Cross Connection Control Policy Handbook
List of Approved Backflow Prevention Assemblies
Change of Mailing Address Request Form

P-35 Backflow Prevention Assembly Overview for Above Ground Installation
P-35-Backflow-Prevention Assembly for Fire Services Standard Drawing