What material is NOT commonly used in plumbing systems?

Steel is not commonly used in modern plumbing systems primarily due to its susceptibility to corrosion and rust over time, which can lead to failures and contamination of the water supply. Instead, materials like copper, rigid plastic, and flexible plastic are preferred for their durability, resistance to corrosion, and lower maintenance requirements.

Copper is widely used in plumbing for its longevity and antibacterial properties, making it an effective choice for water supply lines. Rigid plastic, such as PVC or CPVC, is favored for drain, waste, and vent systems because it is lightweight, easy to work with, and resistant to chemical corrosion. Flexible plastic, often referred to as PEX, offers ease of installation, especially in retrofitting projects, and its flexibility allows it to navigate around obstacles without needing joints, reducing the risk of leaks.

Due to these advantages, the prevalence of copper, rigid plastic, and flexible plastic in plumbing systems makes steel a less common choice.