Which of the following is a characteristic of backed-up siphonage?

Backed-up siphonage is a phenomenon that occurs when there is a reduction in water pressure, leading to the withdrawal of liquid through a drainage system. This situation typically arises when a plumbing fixture, like a sink or toilet, is connected to a vent system that becomes compromised, allowing the creation of a vacuum. Such a reduction in pressure essentially pulls water from nearby fixtures or traps, which can potentially allow contaminants from the drainage system to be siphoned back into the potable water supply.

When water pressure drops, it can create a situation where the air pressure inside the drainage pipes becomes lower than that outside the pipes, leading to the siphoning effect. This characteristic is critical for understanding how siphonage can lead to contamination and the importance of proper venting in plumbing systems to prevent backflow issues.

The other characteristics listed do not correctly describe backed-up siphonage: functioning without negative pressure is contrary to the definition of siphonage, while its impacts on potable water and the temporary nature of the condition also fail to capture the essence of this phenomenon.