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Backflow at premises with irrigation systems

March 12, 2011

DATE OF BACKFLOW INCIDENT: October 1991 LOCATION OF BACKFLOW INCIDENT: Southgate, Michigan SOURCE(S) OF INFORMATION: – Drinking Water & Backflow Prevention, Volume 9 Number 6 (June 1992)
– Pacific Northwest Section of the American Water Works Association, Summary of Backflow Incidents, Fourth Edition, 1995
– Watts Industries, Inc.; Watts Regulator News/Stop Backflow


On October 1, 1991, two homeowners in the City of Southgate, Michigan, found parasitic worms, or nematodes, in their water. One homeowner found the worms swimming around in his bathtub when he started filling the tub for his child. He also found rust and other debris in his water. The Wayne County Health Department determined that water had backflowed through a residential irrigation system into the public water system.

An atmospheric vacuum breaker on the residential irrigation system had malfunctioned because the device’s air inlet valve had stuck to the device’s air inlet port. There was a water main break, which caused a vacuum in the public water system. The vacuum in the public water system sucked some water–and some nematodes–from the irrigation system into the public water system.

Crews from the City’s Department of Public Services opened fire hydrants and flushed all the water mains located three blocks north and south of where the backflow incident occurred. Analysis of subsequent water samples collected by the Department of Public Services showed no detectable coliform bacteria.

The County cited the owner of the irrigation system for improper installation of the system. The contractor that this resident employed to install the irrigation system did not have a City permit and used a “cheap” atmospheric vacuum breaker.

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