Which of the following materials is commonly used for water mains?

Ductile iron is commonly used for water mains due to its excellent strength-to-weight ratio, corrosion resistance, and flexibility. It is particularly beneficial in water distribution because it can withstand high pressure and is less likely to break or suffer from fatigue compared to other materials. Ductile iron pipes are designed to handle the stresses associated with dynamic loads and shifting soil conditions, making them suitable for buried pipelines.

Plastic is often used in some applications, especially for smaller pipelines or in specific environments, due to its corrosion resistance and lower installation costs, but it may not provide the same level of durability as ductile iron under significant pressure. Concrete is generally used for larger infrastructure and storage, such as water treatment plants and reservoirs, rather than for main lines. Asbestos, while it was used in the past for various construction applications, has been largely phased out due to health risks associated with its fibers and is not suitable for modern water distribution systems. Thus, ductile iron remains the preferred material for constructing reliable and long-lasting water mains.