When is field disinfection of distribution system mains and storage reservoirs necessary?

Field disinfection of distribution system mains and storage reservoirs is a critical process to ensure the safety and cleanliness of drinking water. Each situation mentioned in the options underscores when disinfection is necessary.

After repairs are made, there is a risk of introducing contaminants into the system. Disinfection ensures that any pathogens or unwanted substances are eliminated, restoring the system to safe operating conditions.

When distribution systems are new, disinfection is necessary to remove any biological contaminants that may have been introduced during the construction process. New pipelines and reservoirs can harbor harmful bacteria and other pathogens that require eradication before the water is delivered to consumers.

Whenever there is a possibility of contamination, such as following a significant event like a natural disaster, a malfunction, or any instances that disrupt normal operations (like leaks or breaks in the system), disinfection becomes critical. This prevents any serious health risks associated with untreated water entering the distribution system.

Thus, disinfection is essential in all these scenarios to maintain water quality and protect public health. Therefore, the most comprehensive answer encompasses all situations where field disinfection is necessary.