What is the main function of a shut-off valve?

The main function of a shut-off valve is to allow the user to shut off water entering a fixture. This is crucial for maintenance and repairs because it provides a way to isolate plumbing sections without affecting the entire system. For instance, if a sink or toilet needs repairs, the shut-off valve can be used to stop water flow specifically to that fixture, preventing leaks and water damage while the work is being done.

Shut-off valves are typically installed near fixtures and in supply lines, and they can be manually operated. Their importance in a kitchen or bathroom setup cannot be overstated; they enable effective and safe plumbing management.

The other options address functions that are not related to shut-off valves. While increasing water pressure involves different mechanisms, regulating temperature requires a mixing valve. Filtering impurities pertains to water filtration systems, which serve a completely different purpose. Thus, the role of the shut-off valve is distinctly defined, making option B the correct choice.