What is the main line filled with water and under pressure referred to as?

The main line filled with water and under pressure is referred to as a wet tap or hot tap. This terminology is used in plumbing and maintenance contexts to describe a procedure that allows for the connection to a pressurized water line without disrupting service. A wet tap involves the installation of a new fitting or valve while the system is still pressurized, ensuring that there is minimal interruption in water flow.

This process is often essential in maintaining continuous service to buildings or facilities that rely on a constant water supply. For example, if a maintenance worker needs to add a branch line to an existing system, performing a wet tap enables them to do so without draining the entire system, which could inconvenience users.

The other terms like dry tap, pressure tap, and emergency tap refer to different concepts within plumbing. A dry tap typically indicates a line that is not under pressure or does not contain water. A pressure tap usually refers to a point where measurements or monitoring of pressure are taken rather than the connection itself. An emergency tap suggests a system designed for urgent situations, rather than a method for connecting to a main line. Thus, 'wet tap or hot tap' accurately describes the scenario of connecting to a live, pressurized water line.