A cross-connection is formed at any point where a drinking water line connects either to equipment such as boilers or to systems containing chemicals such as:
- Air-conditioning systems
- Fire sprinkler systems
- Irrigation systems
Cross-connection contamination can occur from backpressure, or when the pressure in the equipment or system is greater than the pressure inside the drinking water line. Contamination can also occur when the pressure of the drinking water line drops due to fairly routine occurrences, such as main breaks or heavy water demand. This causes contaminants to be sucked out from the equipment and into the drinking water line, known as backsiphonage.