After a new water main is installed and pressure tested, it should be:

Filling the new water main with a solution of 25 ppm to 50 ppm free chlorine for at least 24 hours prior to flushing is the correct procedure to ensure the water main is disinfected. This practice is vital for preventing the introduction of harmful bacteria and pathogens that could compromise the safety of the drinking water supply. The chlorine solution acts as a disinfectant, effectively killing any microorganisms that may have been introduced during the installation process or that exist within the existing system.

The procedure typically involves first filling the main with water, followed by adding the chlorine solution to maintain the appropriate concentration throughout the system. This disinfection process not only safeguards public health but also complies with water quality standards set by regulatory agencies.

After this period of chlorination, the water main must be adequately flushed and tested to ensure that residual chlorine levels are within acceptable limits before returning the system to service. This ensures that no harmful concentrations of chlorine remain in the water supply while still confirming the disinfection process was effective.

The other options, such as placing the main into immediate service, limiting inspections, or leaving it empty for a week, do not follow proper disinfection and safety protocols that are critical in maintaining the integrity of water distribution systems.