What does "Back-siphonage" refer to in a piping system?

Back-siphonage refers to the phenomenon that occurs in a piping system when a negative atmospheric pressure is created, leading to the reversal of the normal flow direction of water. This condition can happen when there is a sudden drop in water pressure downstream, such as when a water main breaks or during heavy withdrawals of water. When this negative pressure is present, it can draw contaminated water from a source - such as a polluted pond or a storage tank - back into the clean water supply. Understanding back-siphonage is critical for maintaining the safety and integrity of water distribution systems, as it highlights the need for proper protection measures, such as backflow preventers, to safeguard against contamination.

The other options do not accurately describe back-siphonage. The use of siphons for drainage deals with the general operation of siphon systems and does not encompass the specific issue of negative pressure. The direction of water flow is a broader concept and does not specifically address the risks associated with back-siphonage. While the installation of backflow preventers is an important measure to prevent back-siphonage, it does not define what back-siphonage itself is. Thus, the concept of negative atmospheric pressure is central to understanding how back-s