What is Backflow Prevention and Cross-Connection Control? skip to Main Content

What is Backflow Prevention?

What is Backflow?

Backflow, within the context of the drinking water industry, means the reversal of water flow from its normal or intended direction of flow. Whenever a water utility connects a customer to its water distribution system, the intention is for the water to flow from the distribution system to the customer. However, it is possible, and quite common, for the flow to be reversed and flow from the customer’s plumbing system back into the public water distribution system. If cross-connections exist within the user’s plumbing system when backflow occurs then it is possible to contaminate the public water system. 

What is a Cross-Connection?

A cross-connection is a connection of a potable water system to a non-potable system or a system of questionable water quality.

How does Backflow occur?

Backflow may occur simply because the public water system lost pressure. Backflow, reversal of flow from its normal direction, is usually caused by a back-pressure or back-siphonage.

Back-pressure is a condition that manifests itself when the water pressure within an establishment’s plumbing system exceeds that of the water distribution system supplying the water. This back-pressure might be caused by a difference in elevation, by a pump, by a steam boiler, or by other means.

Back-siphonage may occur when the water pressure within the distribution system falls below that of the plumbing system it is supplying. This might happen due to a fire department ‘plumper’ truck pumping water out of the distribution system faster than the water treatment plant equipment can replace it. The water rushing downhill due to a broken water main might create a partial vacuum on some plumbing systems connected in the vicinity of the break and cause a back-siphonage. Perhaps, simply flushing the water pipes to clean them may cause this phenomenon.

How Does the Water distribution System Become Contaminated?

Where backflow occurs and cross-connections are present you have all of the necessary elements for contamination of the plumbing system and subsequent contamination of the public water system:

For example, suppose an automatic lawn sprinkler system is spraying a lawn when all of a sudden a backsiphonage occurs due to a fire truck pumping water or water rushing from a broken water main. The resulting backflow from the lawn sprinkler system will flow into the plumbing system and then into the water distribution system. As the water backflows, it can suck contamination into the lines through the sprinkler heads, such as insects, pesticides, herbicides, fungicides, fertilizer, worms, and other contaminants. Once in the distribution lines, the contamination could go anywhere in the public water system.

Can Cross-Connections be Hazardous?

Yes, in times gone past many disease epidemics were caused by cross-connections between potable water systems and raw river water or lake water piping systems. Epidemics of typhoid and cholera were often caused by backflow occurrences from these sources. People were very ill or sometimes died. A few of the contaminants documented in the literature as caused by cross-connections are:

Untreated river, sea or lake water, pesticides, herbicides, fungicides, propane gas, worm treatment for poultry, boiler water with chemicals, anti-freeze, blood and body fluids from funeral homes, chemicals, water from car wash establishments , dyes, sewage, worms, heavy metals such as arsenic, petrochemicals, water from flush toilets, bacteria cultures from laboratories and others.

This is only a partial list of documented cases of potable water contamination by virtue of cross-connections and backflow occurrences. They still happen every day, somewhere.

What Can be Done to Prevent Contamination of Our Public Water Systems Due to Cross-Connections?

Modern technology has provided us with new tools to prevent backflow from non-potable sources into our public water systems. they are called backflow prevention assemblies; reduced pressure (RP) or double check valve (DC)- type. Unlike the older accepted, non-testable, hardware for preventing backflow such as swing check valves, dual check valves and atmospheric vacuum breakers (which still have their applications), the PR and DC-type backflow prevention assemblies are testable to assure they are in proper working order. Placed at the site of the cross-connection they can protect the plumbing system from contamination. Placed just downstream of a water meter to an establishment, they can protect the public water system from any contamination that may occur within the entire establishment’s plumbing system.


This Q & A information was reprinted from the Arkansas Department of Health.

Tokay Software thanks, John Hedgecock, P.E. for his efforts.

For more info about what Backflow is:

American Backflow Prevention Association: “Questions and Answers About Cross-Connection Control

The Washington Suburban Sanitary Commission: “Residential Customers: Backflow 101

The Washington Suburban Sanitary Commission: “Explaining Cross-Connections, Backflow Prevention, & Safe Drinking Water

American Water Works Association: “Backflow Prevention and Cross Connection Control Resource Community

The University of Southern California: “The USC Foundation for Cross-Connection Control and Hydraulic Research

Tokay Software Logo

Back To Top