What are the two main types of water mains found in distribution systems?

The two main types of water mains found in distribution systems are transmission mains and distribution mains.

Transmission mains are responsible for transporting large volumes of water from sources, such as treatment plants or reservoirs, to various areas within a service region. They are typically larger in diameter and designed to handle significant pressure and flows, facilitating the efficient movement of treated water over long distances.

Distribution mains, on the other hand, are smaller pipes that deliver water directly to consumers. They branch off from the transmission mains and are responsible for distributing water to residential, commercial, and industrial users. This system of distribution is crucial for ensuring that clean water reaches end-users with adequate pressure and access.

The other choices refer to classifications that don't widely represent distinct types of mains in water distribution systems, which is why they do not capture the essential structure of water utility infrastructure we see in most systems.