Backflow & Cross Connection

What is a cross-connection?

Any physical or potential connection between a potable water supply and a hazardous material or one of questionable quality is a cross-connection. 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 a 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 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 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 be concerned?

Backflow will occur when the water pressure in the public water supply is lost, reduced, or if the customer’s water pressure becomes greater than the public supply. Depending on the type of cross connections that exist, contaminates can flow back into the customer’s water system and eventually into the public water supply. In addition to disease and illness, death can result when drinking water becomes contaminated by chemicals such as lead, cyanide, caustics and arsenic compounds. Pesticides and herbicides used widely in the home have also caused death via cross connections. Identifying potential hazards associated with cross connections, and eliminating or protecting against them is the concern of Consolidated Utility District and the local public health agencies. Because almost all water systems have cross connections, the water system personnel must maintain a constant vigil for their detection and elimination.

How can backflow be prevented?

By installing a Consolidated Utility District approved backflow preventer 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 preventers are the reduced-pressure principle assembly and the double check valve assembly.

Why must backflow preventers 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 are tested periodically to ensure they are functioning properly. The customer is responsible for testing of backflow devices. CUD will send a letter and list of approved testers to customers when their devices are due for testing. The testers must be state certified and approved by Consolidated Utility District’s Cross Connection Coordinator or the tests will not be accepted.

What is the most common form of a cross connection?

Ironically, the ordinary garden hose is the most common offender, as it can be easily connected to the potable water supply and used for a variety of potentially dangerous applications.

What is potentially dangerous about an unprotected sill cock?

A sill cock permits easy attachment of a hose for outside watering purposes. However, a garden hose can be extremely hazardous because they are left submerged in swimming pools, lay in elevated locations (above the sill cock) watering shrubs, chemical sprayers are attached to hoses for weed-killing, etc.; and hoses are often left laying on the ground which may be contaminated with fertilizer, cesspools, and garden chemicals.

What protection is required for sill cocks?

A hose bib vacuum breaker should be installed on every sill cock to isolate garden hose applications thus protecting the potable water supply from contamination.

Should a hose bib vacuum breaker be used on frost-free hydrants?

Definitely, providing the device is equipped with means to permit the line to drain after the hydrant is shut-off. A “removable” type hose bib vacuum breaker could allow the hydrant to be drained, but the possibility exists that users might fail to remove it for draining purposes, thus defeating the benefit of the frost-proof hydrant feature. If the device is of the “non-removable” type, be sure it is equipped with means to drain the line to prevent winter freezing.

What is the common difference between pollution and contamination?

Pollution of the water supply does not constitute an actual health hazard, although the quality of the water is impaired with respect to taste, odor, or utility. Contamination of the water supply, however, does constitute an actual health hazard; the consumer being subjected to potentially lethal water-borne disease or illness.

Where is a Double Check Valve Assembly used?

The only place Consolidated Utility’s policy allows double checks to be installed is on fire lines that are classified as low-hazard level.

Where is Reduced Pressure Zone Backflow Preventer used?

Reduced Pressure Zone Assemblies may be used on all direct connections which may be subject to back pressure or back siphonage, and where there is the possibility of contamination by that material the does constitute a potential health hazard.

What are typical applications for Double Check Valve Assemblies?

Double Check Valve Assemblies may be used where the degree of hazard is low, meaning that the non-potable source is polluted rather than contaminated. Local inspection departments oftentimes determine the degree of hazard. Such departments should be questioned in order to comply with local regulations.

What are typical applications for Reduced Pressure Zone Backflow Preventers?

This type should be used whenever the non-potable source is more of a contaminant than a pollutant. Basically, they are applied as main line protection to protect the municipal water supply, but should also be used on branch line applications where non-potable fluid would constitute a health hazard, such as boiler feed lines, commercial garbage disposal systems, industrial boilers, etc.

What is the benefit of a strainer preceding a backflow preventer?

A strainer will protect the check valves of a backflow preventer from fouling due to foreign matter and debris which may be flowing through the line. This not only protects the valve but eliminates nuisance fouling and subsequent maintenance and shutdown. The use of a strainer with a water pressure reducing valve has been an accepted practice for years. The amount of pressure drop attributed to the strainer is negligible and is far outweighed by the advantages provided by the strainer.

State Guidance Concerning Lawn Irrigation Systems on Public Water Systems

Lawn irrigation systems, both commercial and residential, are recognized by the State of Tennessee, Division of Water Supply as an actual and potential cross-connection to a public water system. The contact between the sprinkler heads and the soil or submergence of sprinkler heads allows a connection between the potable water system and water of unknown or unsafe quality.

Soil and standing water in contact with the sprinkler heads poses a significant risk of containing E.coli, Cryptosporidium, Giardia, other pathogens, and hazardous chemicals used for lawn care. Many lawn irrigation systems use toxic chemicals injected in the piping to fertilize and eliminate undesired plants.

Required Protection for Lawn Irrigation Systems on Public Water Systems:

  • For public water systems to protect their distribution lines, lawn irrigation systems are protected by a

Reduced Pressure Principle Assembly or Reduced Pressure Principle Detector Assembly ONLY.

  • Double Check Valves cannot be used for premise isolation on lawn irrigation systems. Double Check Valves may be used for non-health hazards only. Water which contains or may contain pathogens or harmful chemicals is considered a health hazard and must be protected by a Reduced Pressure Principle Assembly or Reduced Pressure Principle Detector Assembly only.
  • Assemblies must be tested annually.
  • Assemblies on lawn irrigation systems must be tested during the start-up period . Annual testing immediately prior to winterization or seasonal shutdown is not acceptable.


When mechanical devices are relied upon to provide protection against backflow, it is necessary to inspect, test, and repair the assemblies on an annual basis. It must be realized that all mechanical devices are subject to fouling and to wear or deterioration, which can render them ineffective and prevent their meeting the performance standard set up for these assemblies. Only individuals who have demonstrated proficiencies and have obtained a Certificate of Competency for Testing and Evaluation of Backflow Prevention Assemblies obtained from the Division of Water Supply and any other requirements set forth by the water system should be utilized.

When do I have to have my Backflow Irrigation tested?

As part of the continuing Cross-Connection Program at Consolidated Utility District, it is necessary to annually test all Backflow prevention devices to insure its effectiveness.  The IRRIGATION backflow prevention device(s) installed on property, owned or controlled by you.

       Division of Water Supply Regulation 0400-45-01-.17(6) REQUIRES ALL irrigation backflows to be tested after installation & during start-up each year. If the irrigation system is turned on and not tested  water service can be disconnected until the device is tested.

Lawn irrigation systems, both commercial and residential, are recognized by the State of Tennessee as an actual high risk health hazard cross-connection. The contact between the sprinkler heads and the soil or rain water allows a connection between the portable water and unsafe water. Soil and standing water in contact with the sprinkler heads poses a significant risk of containing E.coli, Giardia, harmful chemicals and fertilizers.

If you are not planning to use your irrigation system, the backflow device must be removed and the irrigation lines capped and contact Randy Harrell at 615-225-3326.