In a piping system, water is intended to flow in one direction: from the supply to the point of delivery. Danger lurks when the pressure in a system exceeds the pressure of the supply. Anytime pressure in a system drops, even momentarily, the system is subject to backflow, back pressure, or back siphonage, opening the door to contamination. This can happen all too easily when a water main is shut off, a water main is broken, or water demand surges in a specific area. Ultimately, rigorous backflow prevention and competent, thorough testing protect against cross-contamination. Avoiding cross-connections, however, has its challenges, especially considering the vastly more complicated connections to water at sites such as medical and diagnostic centers and research facilities.
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