What is used to check for leaks in a water supply piping system during a hydrostatic test?

In a hydrostatic test for a water supply piping system, water is typically used to check for leaks. This process involves filling the piping system with water and then pressurizing it to a specified level while monitoring for any drops in pressure, which would indicate the presence of a leak.

Water is chosen for this testing method because it is incompressible and readily available, making it effective for accurately assessing the integrity of the piping system under pressure. The ability to easily identify leaks is critical for ensuring the reliability and safety of plumbing installations.

Using water also minimizes the risks associated with other substances, such as gases or chemicals, which could pose safety hazards or complicate the testing process. Thus, the correct answer highlights the standard and safest practice in conducting hydrostatic tests.