What is backflow?
Well, here’s the technical answer. A backflow is the reversal of the normal flow of a liquid or gas.
So, how does a backflow happen? Whenever a cross-connection exists then there is a potential that a hazardous backflow can occur. Undesirable contaminants can enter the water supply, which becomes a health hazard.
What is a cross-connection? Simply stated, a cross-connection is a link between drinking water and a non potable system. Potable water is safe to drink and non potable water has other uses and quality.
Here’s an example of a backflow incident that happened in Wilson, North Carolina.
DATE OF BACKFLOW INCIDENT: November 1993
LOCATION OF BACKFLOW INCIDENT: Wilson, North Carolina
SOURCE(S) OF INFORMATION:
– Drinking Water & Backflow Prevention, Volume 11 Number 2 (February 1994)
– Pacific Northwest Section of the American Water Works Association, Summary of Backflow Incidents, Fourth Edition, 1995
CASE HISTORY
On November 17, 1993, the Wilson, North Carolina, Water Distribution Division received a complaint from a clinic. The clinic was complaining about a strange, bitter taste and strong chemical odor to its water. Upon investigation, the City Water Distribution Division discovered that chemicals from a mixer used in x-ray development had backflowed into the clinic’s potable water system.
A chemical mixer used in x-ray development at the clinic combined water with chemicals–developer and fixer. Water was added to the mixer using a garden hose connected to a hose bibb. Someone submerged the end of this garden hose in the mixer and, thus, created an indirect cross-connection. A hose bibb vacuum breaker was not in place on the hose bibb as required by code, although such a device had been in place when the local building department issued the final certificate of occupancy for the clinic.
On November 15, 1993, City Water Distribution Division personnel, working with a utility contractor, cut a section from the eight-inch-diameter water main in front of the clinic to replace a leaking tapping sleeve with a tee. They did this work during evening hours because the clinic would lose water service temporarily. While this work was being done, a negative pressure apparently developed in the water supply piping to or in the clinic. As a result, the chemicals in the mixer were backsiphoned through the garden hose mentioned above and into the clinic’s potable water system.
http://www.treeo.ufl.edu/backflow/epa-resources/backflow-case-histories/#b
So you can see how a pathway was created with a physical link of a garden hose between potable water and a non potable system.
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