Backflow Prevention and
Cross Connection Control

Learn about Cross-Connections

A cross-connection is any faulty plumbing connection to a potable water supply system through which potable (drinking) water is supplied to a service outlet and through which contaminants unfit for human consumption can enter the potable water lines by back pressure or backsiphonage backflow.

During a backflow event, these contaminants could be drawn or pushed back into the potable water distribution system. The pollution from a cross-connection can cause the water to become aesthetically unappealing, creating problems such as strange tastes, odors, and/or colors. A cross-connection can also allow a contaminant to enter the potable water lines, causing illness or death to those who consume contaminated water.
Methods in which a cross-connection occurs:

• A contaminant or pollutant source is plumbed into a potable water line, or
• A contaminant or pollutant enters a water line through a break or opening.

Example of an inadvertent cross-connection:

Placing a hose directly into a container where the chemicals and water can mix may be all it takes to inadvertently introduce harmful chemicals into your drinking water. How?

• Faulty Plumbing Connection: The chemicals in the tank can enter the outlet end of the submerged water hose and potentially contaminate the water system. Once the toxic solution enters the plumbing or public water line it can be potentially consumed or used by unsuspecting people.
  
• Pipeline Break: When a pipe break or opening occurs, there is a loss of water pressure in the pipe distribution system. As a result of loss of pressure, a backflow event may occur when the non-potable water is backsiphoned into the pipe distribution system.

Solutions for repairing a cross-connection:

Avoid placement of a hose directly into any containers, especially when using chemicals. Instead, simply hold the hose above the opening or install a permanent air gap assembly.

Direct pipe cross-connections are prohibited due to the inherent threats to the safety of our water system. It's easy to eliminate a cross connection if you discover it by disconnecting the pipe and re-routing it/re-plumbing it. As a last resort, installation of an approved backflow prevention device will provide a viable solution.

Backflow Prevention:
The best way to prevent a backflow event is by maintaining an air-gap between the potable water supply pipeline and an open or non-pressure receiving vessel. The District requires inspection and approval (from the Backflow Program office) of an air-gap before it may be utilized for commercial purposes. In many cases, however, an air-gap is not a practical solution. In those cases, one of the following backflow prevention devices must be installed to prevent the undesirable reversal of flow of water or mixtures of water into the distribution pipes of the potable water supply.

There are three main types of backflow prevention devices which are widely used:

Reduced Pressure (RP) Device

An RP is generally used as a containment device, however it can also be used as an isolation device. It is designed to protect against non-health hazards (pollutants) and health hazards (contaminant).

Here's some examples of infrastructure requiring the use of an RP device:

Cooling System
Filter/Softener Backwash Water
Cooling Tower
Reservoir
Circulating System
Industrial Fluid System
Fire Sprinkler System (if used with chemicals)
Plating Facility

an RP device in use

Requirements:

• ALWAYS check with your local plumbing departments and water suppliers before beginning installation.
• When installing the device, a minimum of 12 inches of access and clearance between the lowest portion of the device and grade, floor or platform must be provided.
• Assemblies higher than 5 feet above the floor must have a permanent platform adequate to test the device.

schematic of an RP device click for larger image

• Assemblies must have adequate clearances around the assembly so that testing and repairs can be made.
• Assemblies cannot be installed in direct connections between potable systems and sewage.
• Assemblies cannot be installed in areas that are subject to toxic or corrosive fumes or vapors.
• Assemblies cannot be installed in areas where the assembly may become submerged.
• Assemblies cannot be installed above electrical outlets, circuit breakers, electrical space heaters or any other electrical use where discharge from the assembly while testing or repairing may cause a hazard.
• Assemblies cannot be installed in false ceilings or other areas where the assembly is out of sight.
• Assemblies cannot be installed in basements, unless there is drainage equal to two times the pipe diameter (see Air-Gap(link)) or a high water alarm is installed near the device.
• Assemblies cannot be installed in manholes or vaults. Some confined space installations are allowed.
• Assemblies cannot be installed in any area where water spillage during normal testing and repairs could cause a problem.
• Orientation (see Approved RP Backflow Devices for correct orientation upon installation)

Double Check (DC) Valve Device

Generally used as an isolation device on fire lines. Can only be used to protect against a non-health hazard (pollutant).

Requirements:

• ALWAYS check with your local plumbing departments and water suppliers before beginning installation.
• When installing the device, a minimum of 1 foot of access and clearance between the lowest portion of the device and grade, floor or platform must be provided.
• Assemblies higher than 5 feet above the floor must have a permanent platform adequate to test the device.
• Assemblies must have adequate clearances around the assembly so that testing and repairs can be made.
• Assemblies cannot be installed in health hazard systems.
• Assemblies cannot be installed in areas where the assembly may become submerged.

schematic of a DC device click for larger image

• Assemblies cannot be installed above electrical outlets, circuit breakers, electrical space heaters or any other electrical use where discharge from the assembly while testing or repairing may cause a hazard.
• Assemblies cannot be installed in manholes or vaults. Some confined space installations are allowed.
• Assemblies cannot be installed in any area where water spillage during normal testing and repairs could cause a problem.
• Orientation (see Approved DC Backflow Devices for correct orientation upon installation)

Generally used as an isolation device on irrigation systems. These are designed to protect against non-health hazard (pollutant) or a health hazard (contaminant) under a backsiphonage condition only.

Requirements:

• Must be installed 12” above the highest piping in the system.
• This ensures that backpressure due to elevation is not created.
• The device cannot be installed more than five feet above ground.
• Must be installed in situations where the device will undergo continuous supply pressure for long periods.

a PVB device in use click for larger image

• Can only be used as an isolation device, unless the device is installed on an irrigation system served by a separate service line.
• Orientation (see Approved PVB Backflow Devices for correct orientation upon installation).

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