Texas Commission on Environmental Quality (TCEQ). Class C Water License Exam

What chlorine dosage is required for disinfecting a new or repaired water line?

1. 25 mg/L

2. 50 mg/L

3. 75 mg/L

4. 100 mg/L

The correct answer is: 50 mg/L

For disinfecting a new or repaired water line, the required chlorine dosage is typically 50 mg/L. This dosage is effective in ensuring that any potentially harmful pathogens present in the water are effectively eliminated. The use of 50 mg/L as a standard dosage is based on guidelines from regulatory bodies, which take into account factors such as the volume of water, the flow rate, and the specific types of bacteria or viruses that may be present. Chlorine serves as a powerful oxidizing agent that kills bacteria and inactivates viruses. This specific dosage has been found to be sufficient for basic disinfection purposes while also ensuring that the residual chlorine remains in the system long enough to provide continued protection against contaminants, thus promoting safe drinking water. Higher dosages, like 75 mg/L or 100 mg/L, may sometimes be used in specific scenarios or for special requirements, but the standard dosage for typical disinfection practices during construction or repair is aligned with the 50 mg/L recommendation. Lower dosages such as 25 mg/L may not offer adequate protection against all pathogens during the initial disinfection phase.