What type of valve is required on all water supply lines to fixtures?

The requirement for a shut-off valve on all water supply lines to fixtures is based on plumbing codes that prioritize ease of maintenance and emergency repairs. A shut-off valve allows for the quick stopping of water flow to a specific fixture without affecting the water supply to the entire system. This is crucial during repairs or when a fixture malfunctions, as it minimizes water damage and allows for efficient work to be conducted.

In many plumbing practices, maintaining the ability to isolate water flow is seen as critical for safety and functionality. While a ball valve is effective and commonly used, it is often categorized under the broader umbrella of shut-off valves. Therefore, the term "shut-off valve" encompasses a variety of mechanisms, including ball valves, but it specifically emphasizes the functionality of stopping water flow.

Additionally, check valves and pressure relief valves serve different purposes in plumbing systems. Check valves are designed to prevent backflow, ensuring that water flows in only one direction, while pressure relief valves are crucial for regulating pressure within a system, preventing potential bursts or leaks. These valves do not fulfill the specific need for turning off water selectively to a fixture, which is why they do not meet the requirement stipulated in the question.