Question 4

The solution MUST remain in the system for 24 hours.

To ensure effective disinfection, the water-chlorine solution containing 50 parts per million of chlorine must remain in the potable water system for 24 hours.

A) 8 hours

While an 8-hour duration may provide some level of disinfection, it is insufficient for a chlorine concentration of 50 parts per million. The effectiveness of chlorine in killing pathogens requires a longer contact time to ensure safety and compliance with health standards.

B) 12 hours

A 12-hour duration is still below the required contact time for 50 parts per million of chlorine. Although it may enhance disinfection compared to a shorter duration, it does not meet the necessary standards for ensuring the complete elimination of harmful microorganisms.

C) 24 hours

This option is correct as it meets the recommended contact time for chlorine disinfection at this concentration. Allowing the solution to remain in the system for 24 hours ensures adequate exposure time for effective disinfection, thereby safeguarding public health.

D) 36 hours

While a 36-hour exposure might seem more effective, it exceeds the necessary duration for a chlorine concentration of 50 parts per million. Prolonged exposure may not provide additional benefits and could potentially lead to other issues, such as chlorine byproducts that may be harmful.

Conclusion

The correct answer is 24 hours, as this duration ensures effective disinfection of the potable water system with a chlorine concentration of 50 parts per million. Other options fall short in providing sufficient contact time, while excessive durations like 36 hours are unnecessary and could introduce other complications. Proper adherence to the 24-hour guideline is crucial for ensuring water safety and compliance with health regulations.