What is a common issue that can occur from improper venting in a plumbing system?

Improper venting in a plumbing system can lead to slow drainage or gurgling noises, which is a common issue that arises when vents are either blocked or incorrectly installed. Vents are essential for allowing air to enter the plumbing system, which helps maintain the proper pressure needed for wastewater to flow freely. When venting is inadequate, it creates a vacuum that restricts the flow of water, resulting in slow drainage. Additionally, as the system struggles to equalize pressure, it can create gurgling sounds in the pipes as water and air mix improperly.

The other choices, while potentially serious issues in plumbing systems, do not specifically stem from improper venting. Leaking pipes typically result from corrosion, damage, or poor connections. Clogged fixtures often result from blockages due to debris or buildup rather than venting problems. Water contamination is usually related to issues with the quality of water supply or backflow, not directly associated with venting practices. Thus, the correct choice highlights a direct consequence of improper venting, making it the most relevant answer.