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(See endnote 35)

A cross-connection is a place in the system where non-potable water is connected to potable water sources. This may result in a backflow of the non-potable water into the potable water because of reduced pressure, called backsiphonage, which may occur when the pressure of the non-potable water is greater than the pressure of the potable water. This condition may occur because of main breaks, flushing of the mains, pump failure, loss of electricity, unusual increase in customer demand, booster pumps in high-rise buildings, and emergency firefighting needs. This type of illegal connection can be found in industrial plants, heating and cooling units, waste disposal systems, etc. A submerged inlet occurs when a source of potable water is below a container which has non-potable water in it. For example, if someone puts a hose on a faucet and allows it to fall below the accumulated non-potable water in the container, then a break in pressure in the potable water supply would suck the non-potable water back up through the pipe and into the potable water. Cross-connections and submerged inlets have caused numerous outbreaks of waterborne diseases in people.

Best Practices for Avoiding and Correcting Cross-Connections and Submerged Inlets

  • • Maintain an operating pressure of 20 pounds per square inch at all locations in a water distribution system at all times.
  • • To avoid intentional contamination of the water distribution system, homeland security recommends physical security measures be taken to prevent someone from introducing chemical or biological contaminants through cross-connections and backflow.
  • • Create a comprehensive public education program for communities teaching them how to prevent cross-connections and submerged inlet problems from occurring.
  • • Create or, if the program already exists, enhance a major cross-connection inspection program for all facilities where chemical or biological contaminants can enter the water distribution system. This program should be enforced by law and penalties should be applied if situations are not corrected immediately upon their discovery.
  • • Create a comprehensive training program for all individuals involved in new construction, maintenance, or repairs related to the water distribution system, which may cause possible cross-connections, in residential, industrial, and commercial facilities. Make this action part of continuing education requirements for all plumbers and other individuals involved in the connection of pipes in relationship to the water distribution system.
  • • Never submerge a garden hose in a chemical mixing tank since this constitutes a submerged inlet and in the event of a pressure change in the fresh water line, there may be serious backsiphonage problems.
  • • Never establish a cross-connection between an irrigation system and the potable water supply because a vacuum breaker valve used to protect the potable water supply could fail and create substantial problems with microorganisms or chemicals.
  • • Evaluate all connections to cooling towers between the potable water supply and storage facility. This is a common area where contamination may occur and the potable water supply may become contaminated.
  • • When cleaning out any type of medical equipment, air conditioning systems, etc., do not insert a hose containing potable water into the equipment because of a potential break in pressure resulting in backflow of the contents into the drinking water supply.
  • • Report all incidents of reduced pressure in the potable water distribution system to the water companies and the health department in the event that this may be the reason for an outbreak of waterborne disease.
  • • Use mechanical backflow prevention devices in water distribution systems at the service connection to a facility. These devices may include pressure vacuum breakers, double check valve assemblies, and spill-resistant vacuum breakers. They also include air gaps.
  • • Use physical separation as in air gaps to prevent backflow from occurring between the potable water system and the non-potable source. This means there needs to be a separation of the supply pipe from the overflow rim of a receptacle which is twice the diameter of the incoming supply pipe. In that way, water cannot possibly flow back through the supply pipe.
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