a skilled plumber carefully connects a large metal pipe to an existing water main underground. He uses a wrench to tighten the joint as water flows through the transparent section. The connected pipe immediately begins carrying clean water from the main line toward nearby buildings. Water rushes through the pipe system in a visible stream showing the flow direction. Other construction workers observe the successful connection while pointing at the steady water flow. A supervisor nods approvingly as the pipe system begins functioning properly. pipes being used to convey water and other fluid substances through a distribution system