What does back-siphonage refer to in plumbing?

Back-siphonage refers to a situation in plumbing where there is a negative pressure created in a water supply system, causing contaminated water to be drawn back into the clean water supply. This typically occurs when there is a sudden drop in water pressure, such as during a fire hydrant opening or a large water demand elsewhere in the system. The resulting vacuum can siphon liquid from a plumbing fixture or system where contaminants are present, thereby risking contamination of the potable water supply.

Understanding back-siphonage is critical in maintaining safe drinking water standards, as it highlights the importance of proper backflow prevention measures, such as installing vacuum breakers or air gaps in areas susceptible to contamination.