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User Answers:

1. A cross-connection is a (unintentional) connection between a (good/clean) public water system or consumer's potable (i.e., drinking) water system and any source or system containing nonpotable (bad) water or other non drinkable substances.
   
   An example is the piping between a public water system or consumer's potable water system and an auxiliary water system, cooling system, or irrigation system. Backflow preventers are used to stop cross connections.   [edit]
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