Many water utilities spend considerable money, effort and time to protect water sources from contamination and to treat source water, only to have contamination enter the system through a cross connection. This is usually caused by a reversal in the normal direction of flow in the piping, most commonly through Backsiphonage or Backpressure. Backsiphonage is caused by negative pressure or reduced pressure in the water supply piping. Consider the following example: if a hose attached to a faucet is submerged in a liquid chemical and the pressure is reduced due to a waterline break or opening a fire hydrant, a siphoning action could cause the liquid chemical to flow back through the hose and into the water main. Backpressure occurs when a potable water system is connected to a nonpotable system which operates at a higher pressure. In this example, a ship is connected to a community water system while in port. The ship's fire fighting system uses the river water as a source but is also connected to the community water system via the ship's plumbing. If there is non-existent or inadequate separation between these two systems and the high-pressure fire line is activated, river water will flow into the community water supply.
Cross connections must either be physically disconnected or have an approved backflow prevention device installed to protect the public water system. The five types of approved devices are:
All public water system operators are required to maintain an active cross connection control program to identify, eliminate or isolate all cross connections within their systems. This program should provide for inspections of premises, installation of approved backflow devices and annual testing of installed devices.