Water Contamination From Backflow?

Water Contamination From Backflow?

[This article, written by the American Ground Water Trust was originally published in


Water Contamination From Backflow?

Backflow is water is flowing in pipes/plumbing/hoses in the opposite direction from its normal flow. If the direction of flow is reversed, because of a change in pressures, backflow could allow contaminants to enter a drinking water system.  A similar contamination risk can occur from cross-connections. A cross-connection exists when plumbing systems are configured in such a way that any source of non-drinkable water or other substances can enter the piping system of a drinking supply.  [Plumbing and building codes prohibit the cross-connection of well supply and utility supply.]


Pressure changes in pipes and water distribution systems can result from breaks in electrical supply, pipe failure or excessive use of water from fixtures connected to the same piping system, (especially if there are down-gradient uses that may cause a siphon-effect).


Backflow risks can easily be avoided by installing simple plumbing fittings.  There is plenty of information on the subject that can easily be accessed by homeowners.  First ask yourself the following questions:


1. Have you ever used a hosepipe to:

·       Fill a swimming pool?

·       Flush a car radiator?

·       Fill a fishpond?

·       Fill a container to shampoo your dog?

·       Supply water to horses or other farm animals?

·       Flush out a blocked water drain or septic line?

·       Mix garden chemicals in a bucket?

2. Do you recycle your home’s gray-water (from laundry or shower) to irrigate shrubs or garden beds?

3. Do you have a water well and are you connected to a utility supply?

4. Do you have a lawn sprinkler system?


If the answer is yes to any of the above questions you should check that you have a backflow prevention device between your hose and hose bib (spigot or outside faucet, tap). The basic means of preventing backflow is by creating an air gap, which provides a barrier to backflow.

Probably over half of the reported backflow and cross-connection problems involve garden hoses. Without a backflow prevention device, the contents of the hose and anything it is connected to, have the potential to backflow into the piping system and contaminate your drinking water.


A hose-bib vacuum breaker is a simple, inexpensive screw-on device that can be purchased at plumbing or hardware stores.  Homeowners should check that all taps (faucets, spigots) to which a hose may be connected are fitted with hose bib vacuum breakers.  They only cost a few dollars each and can be installed by a homeowner.  A more effective backflow prevention device called an atmospheric vacuum breaker costs about $50 and should be installed by a qualified plumber who understands water flow hydraulics.


If you don’t have a backflow prevention device – talk to a plumber or water system installation specialist.  For examples of backflow occurrences and for more information about prevention, visit the website (and links page) of the American Backflow Prevention Association at http://www.abpa.org


[© American Ground Water Trust.  This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2003, Number 1]