Backflow Prevention Frequently Asked Questions

What is a cross-connection?

Any physical or potential connection between a potable water supply and a hazardous material or one of questionable quality. There shall be no such connection without the installation of an approved backflow prevention assembly in accordance to the degree of hazard of the substance involved.

What is backflow?

Backflow is the undesirable reversal of flow of non-potable water or other substances through a cross-connection and into the piping of a public water system or consumer's potable water system. There are two types of backflow--back pressure and back siphonage.

What is back pressure backflow?

Back pressure backflow is backflow caused by a downstream pressure that is greater than the upstream or supply pressure in a public water system or consumer's potable water system. Back pressure (i.e., downstream pressure that is greater than the potable water supply pressure) can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both. Increases in downstream pressure can be created by pumps, temperature increases in boilers, etc. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds that amount of water being supplied, such as during water line flushing, fire fighting, or breaks in water mains.

What is back siphonage?

Back siphonage is backflow caused by a negative pressure (i.e., a vacuum or partial vacuum) in a public water system or consumer's potable water system. The effect is similar to drinking water through a straw. Back siphonage can occur when there is a stoppage of water supply due to nearby fire fighting, a break in a water main, etc.

Why do water suppliers need to control cross-connections and protect their public water systems against backflow?

Backflow into a public water system can pollute or contaminate the potable water in that system (i.e., backflow into a public water system can make the water in that system unusable or unsafe to drink), and each water supplier has a responsibility to provide water that is usable and safe to drink under all foreseeable circumstances. Furthermore, consumers generally have absolute faith that water delivered to them through a public water system is always safe to drink. For these reasons, each water supplier must take reasonable precautions to protect its public water system against backflow.

How can backflow be prevented?

By installing an approved backflow preventer. A backflow preventer is a means or mechanism to prevent backflow. The basic means of preventing backflow is an air gap which either eliminates a cross-connection or provides a barrier to backflow. The basic mechanism for preventing backflow is a mechanical backflow preventer, which provides a physical barrier to backflow. The principal types of mechanical backflow preventer are the reduced-pressure principle assembly, the pressure vacuum breaker assembly, and the double check valve assembly.

A Lincoln Water System approved backflow preventer means one of the following:

Approved air gap

An air gap is a vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel. This separation must be at least twice the diameter of the water supply outlet and never less than one inch. An air gap is considered the maximum protection available against back pressure backflow or back siphonage, but is not always practical and can easily be bypassed.

Approved air gap air gap

Double check backflow assembly (DC)

A DC is a testable mechanical backflow preventer that consists of two independently acting, spring-loaded check valves. It includes shutoff valves at each end of the assembly and is equipped with test cocks (required to be tested annually by a State Certified Grade 6 Operator) against back pressure backflow and back siphonage, but should be used only on non-health hazards.

Double Check Backflow Assembly Double Check Backflow Assembly

Reduced pressure principle backflow assembly (RP)

An RP is a testable mechanical backflow preventer that consists of two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve between the check valves and below the first check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks (required to be tested annually by a State Certified Grade 6 Operator). An RP is effective against back pressure backflow and back siphonage, and may be used on health or non-health hazards.

reduced pressure principle assembly reduced pressure principle assembly

Pressure vacuum breaker assembly (PVB)

A PVB is a testable mechanical backflow preventer that consists of an independently acting, spring-loaded check valve and an independently acting, spring-loaded air inlet valve on the discharge side of the check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. A PVB may be used to isolate health or non-health hazards, and is to be installed 12-inches above highest downstream water discharge. It is effective against back siphonage only and is most commonly used on lawn sprinkler systems.

pressure vacuum breaker assembly pressure vacuum breaker assembly

Atmospheric Vacuum Breaker (AVB)

An AVB is a non-testable mechanical backflow preventer with a gravity opening poppet air opening, designed to admit atmosphere into the downstream sides of the unit under a no flow condition to prevent back siphonage. It must be installed 6-inches above highest downstream water discharge. There shall be no valves or reduction of pipe size on its downstream side. (Note: This device is installed on certain equipment that uses potable water by the manufacturer or contracted installer. Examples of this equipment are dishwashers, soap dispensers, faucets and deep sinks, etc.) It is up to the City of Lincoln that has jurisdiction to determine which type of backflow protection is required based on the degree of hazard that the property represents to the potable water supply.

Atmospheric Vacuum Breaker Atmospheric Vacuum Breaker

Why do backflow preventers have to be tested at least once annually?

Mechanical backflow preventers have internal seals, springs, and moving parts that are subject to fouling, wear, or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow preventers have to be tested periodically to ensure that they are functioning properly. A visual check of air gaps is sufficient, but mechanical backflow preventers have to be tested by a State Certified Grade 6 Operator, with properly calibrated gauge equipment.

How do I know if I need a backflow prevention assembly?

A member of the cross-connection control staff will send a questionnaire and/or visit your property to perform a premise survey for backflow requirements. You will receive a letter providing you with the guidelines and what action you need to take to ensure compliance with the City of Lincoln requirements.

What is potable water?

Water which is safe for human consumption, free from harmful or objectionable materials as described by the Health Authority.