Backflow & Cross Connection Information

What is Backflow and how does it relate to Cross-Connections?

General Information

The City of Longmont strives to protect our water system from contamination that could diminish our water quality. By installing and maintaining backflow assemblies, the possibility of contaminated water returning to the distribution lines is prevented. You can help keep our water system safe by installing, maintaining and testing your backflow prevention assemblies within the timeframe designated by the City.

What is Backflow?

Backflow refers to an event that causes water to flow in the opposite direction than it is intended for in any pipeline or plumbing system due to pressure fluctuation in private and public water systems. This undesirable reversal of flow may cause potentially non-potable fluids or other substances through a cross connection to enter the public drinking water system or the consumer’s potable water system. Backflow can occur due to back pressure from a downstream source from the water supply or negative pressure in the water supply also known as back siphonage.

Back Siphonage: Negative pressure in the city’s water system can draw in water from a private water system. Negative pressure in the City’s water system can be caused by water main breaks, fire hydrant flushing, or firefighting.

Back Pressure: If pressure in the private water system exceeds the city’s water system pressure, it can force water from the private system into the city’s system. This is usually caused by a privately owned pump used to increase pressure inside a single structure.

Diagram of Back Siphonage where reverse water flow is caused by a loss of water supply pressure and back pressure which is an increase in water pressure that raises the system pressure above the supply pressure.

What is a Cross-Connection?

Cross-connection is a term used by the plumbing and water supply industry to describe a physical pipe connection that could allow a pollutant or contaminant to be drawn or pushed back into the public water system during a backflow event.

Domestic: Domestic service lines are lines that feed the general use of the facility, typically for use in a building. The domestic service line and subsequent plumbing within the building are a private water system, owned and maintained by the property owner. There can be a variety of cross-connections off of a domestic service line, such as permanent swimming pools, industrial water using equipment, and boilers.
Irrigation: Some irrigation lines are tapped directly off of the Public Water Main. In these cases the only cross-connection for this service connection is the irrigation system. Sometimes the irrigation line branches off of the domestic service connection. In this case, the irrigation system is evaluated as one section of the domestic service connection.
Fire Suppression System: Many times fire suppression systems are tapped directly off of the Public Water Main. In some cases, the domestic service line branches off of the fire suppression system service line. Fire suppression systems are a cross-connection for a couple of reasons. First, there may be chemicals added to the fire suppression system that need to be controlled. Second, water in some types of fire suppression systems can be stagnant, allowing bacteria to grow.

The Cross-Connection Threat: When an imbalance of pressure between fresh water supply and a contaminated source pulls contaminated water into the fresh water supply.

Protection through Containment & Isolation Backflow Assemblies

The City of Longmont’s Backflow Prevention and Cross-Connection Control Program mainly revolves around containment assemblies (or devices). This ensures the protection of the drinking water within the public water system. The responsibility for protecting the safety of our public water system belongs to both the water utility and the consumer. There may be cases where, in addition to the containment assemblies, isolation assemblies are used to protect the drinking water quality within the private water system. In limited circumstances and with adequate justification, the City will allow isolation assemblies for compliance with the Backflow Prevention and Cross-Connection Control Program.

Containment: A backflow assembly on the incoming line or service line is containment. The device is after the water meter, but before any branches or connections to the service line.

Isolation: A backflow assembly after branches or connections to the service line. Isolation assemblies are used to protect the drinking water quality within the private water system.

Types of Backflow Control

Assembly (Device): Backflow Prevention Assemblies are mechanical assemblies (devices) installed on the water line to prevent a backflow event. Assemblies are testable and require at least annual testing; those test results must be reported to the City.

Method: Backflow Prevention Methods are methods (such as air gaps) or non-testable devices. Methods are required to be inspected at least annually; those inspection results must be reported to the City.

Types of Backflow Assemblies

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1. Reduced Pressure Principle Assembly (RP)

Used on health hazards in buildings and is a combination of check valves and an air inlet allowing water from the private system to vent when City pressure drops.

Requirements

1 foot above the floor
No higher than 5 feet
Adequate drain
Adequate protection from vandalism if outdoors
Protect from freezing

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2. Pressure Vacuum Breaker (PVB)

Mainly used for irrigation. It has a one way check and a spring loaded air inlet valve that closes when City water main pressure drops.

Requirements

No backpressure
12″ above high point of use
Adequate protection from vandalism if outdoors
Protect from freezing

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3. Double Check Valve Assembly (DCVA)

Typically used on non-health hazards in buildings and on fire lines. It uses two spring loaded valves.

Requirements

12″ above the floor
No higher than 5 feet
Protect from freezing

Requirements

Not under continuous pressure for more than 12 hours
No downstream valves
No backpressure
Six inches above high point of use
Protect from freezing

Air Gap Backflow Method

Used mainly on tanks and faucets, it is a gap between the pipe and the container.

Requirement

The gap needs to be a minimum 2 times the supply pipe diameter