Immediately after filling the water supply piping system with water during a hydrostatic test, what is the next step?

After filling the water supply piping system with water during a hydrostatic test, the next step involves addressing any potential air pockets that may be trapped in the system. Opening valves at high points in the piping allows any air that is trapped to escape, ensuring that the system is completely filled with water. This is crucial because air pockets can affect the accuracy of the hydrostatic test and may lead to misinterpretation of the system's integrity.

Confirming that the system is free of air ensures that the pressure readings taken later will be accurate and that any potential weaknesses in the system can be properly assessed during the test. Therefore, opening valves at the high points is an essential step before proceeding with other actions such as measuring water pressure or checking for leaks, as it sets the foundation for a reliable hydrostatic test.