A repaired water main need to be disinfected and activated within 30 hours. What is the minimum water/chlorine solution that must be put into the main?

The minimum water/chlorine solution required to disinfect a repaired water main is established to ensure effective eradication of pathogens and to maintain safe water quality standards. A concentration of 50 parts per million (ppm) is specified as sufficient for this purpose.

This concentration strikes a balance between effective disinfection and safety for human consumption after the water main is fully flushed and tested. Chlorine at this level is proven to effectively kill bacterial pathogens, which is critical after repairs that might expose the system to contaminants.

When a higher concentration is used, such as 75 or 100 ppm, while it may provide increased disinfection efficacy, it can create higher residual levels that may require more extensive flushing and testing to ensure the water is safe for human consumption. Therefore, the 50 ppm standard is both effective and manageable within the 30-hour timeline for activating the repaired water main.