What is a potential consequence of improper ventilation in a plumbing system?

Proper ventilation in a plumbing system is crucial for maintaining the system's integrity and safety. One of the significant consequences of improper ventilation is that traps may empty due to siphoning. Traps are designed to hold a small amount of water to create a seal against sewer gases. When ventilation is inadequate or blocked, negative pressure can occur, causing the water in the trap to be siphoned out. This loss of water allows harmful sewer gases to enter the home, which can pose health risks and unpleasant odors.

In contrast, while increased water pressure can be an issue in a plumbing system, it is not primarily a consequence of ventilation problems. Contamination of water is typically related to issues like cross-connections or backflow, but not directly linked to ventilation. Water heater malfunctions can arise from various factors, such as sediment buildup or mechanical failure, but again, they are not directly a result of improper ventilation. Thus, the correct understanding of the role that ventilation plays in plumbing systems highlights why the option relating to traps and sewer gases is the correct answer.