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Backflow
What is backflow and how can it be occur?
Backflow is the reversal of normal flow in a system due to backsiphonage or backpressure.

Backsiphonage backflow occurs when a vacuum is induced on a piping system, just like drinking from a glass with a drinking straw. A garden hose or a hose connected to a laundry tub can act as a "drinking straw" allowing undesirable liquids to be drawn through it by backsiphonage. Some typical situations that cause backsiphonage action include:

  • watermain breaks or repairs occurring in the system at a point of lower elevation than your service point.
  • high water flow rates exerted on a watermain due to fire fighting, hydrant flushing, large system demands or major piping breaks.
  • booster pumps taking direct suction from potable water supply piping.
  • undersized piping.

Whenever the drinking water supply system is directly connected to another piping system or process that operates at a higher system pressure, backpressure backflow can occur. 

Typical causes of backpressure backflow include:

  • nonpotable piping systems equipped with pumping equipment (irrigation well interconnected with a potable system, for example).
  • steam or hot water boilers.
  • heat exchangers.


What can be done?
Homeowners, as well as plant managers, businesses, administrators, and school officials, must share the responsibility to protect potable water piping systems from contamination through cross connections. Each should contact either the local water utility or the local health department for assistance in locating and correcting cross connection hazards. Residents supplied by private water well sources must assume total control of their water system and safeguard it from contamination. 

  • First, keep all hoses and faucets away from direct contact with possible contaminants. Never submerge hoses in buckets, pools, tubs, or sinks. In the event of loss of water pressure, you need an air gap. Otherwise the hose will act like a straw and suck the liquid backwards.
  • Second, protect yourself by installing inexpensive backflow protection devices on all hoses and threaded faucets in your home. These devices are available at hardware and home improvement stores for about $5-10 each. Backflow vacuum breakers provide safety valves that prevent liquids from flowing backwards into a hose or faucet.

Specialized backflow prevention devices are available for more elaborate installations, such as built-in lawn irrigation sprinklers, hot water boilers, in-ground swimming pools, heat exchangers, active solar heating systems, private wells, and specialized commercial locations such as dry cleaners, car washes, laboratories, and manufacturers. Backflow devices ensure that potentially contaminated water cannot be drawn back into the public water supply from a business or residence in the event of a negative water main pressure situation.



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