Arizona Plumbing Practice Exam

What causes backflow due to siphonage?

1. When pressure increases

2. When negative pressure develops

3. When water is frozen

4. When pipes are clogged

The correct answer is: When negative pressure develops

Backflow due to siphonage is caused by the development of negative pressure in a plumbing system. This negative pressure creates a condition where the water in the supply line is effectively "pulled" back toward a lower pressure area. Siphonage often occurs when water is drained from a system, creating a vacuum that can draw contaminants or water from other parts of the system, such as a sink or toilet, back into the potable water supply. If, for instance, a large quantity of water is suddenly emptied—like when a toilet is flushed or a fire hydrant is opened—this can result in negative pressure forming in the supply pipes. This negative pressure will draw water from adjoining sources if a connection exists, leading to backflow. Other options do not directly relate to the mechanics of siphonage. While increased pressure and freezing water can cause other issues in plumbing systems, they do not contribute to backflow via siphonage. Clogged pipes can lead to backups but do not create the necessary conditions for siphonage to occur. Understanding these principles is crucial for maintaining safe and effective plumbing systems.