When disinfecting water wells using free chlorine, what is the recommended exposure time and concentration?

The recommended exposure time and concentration for disinfecting water wells using free chlorine is 6-12 hours at a concentration of 25 mg/l. This guideline is aimed at ensuring that sufficient contact time allows the chlorine to effectively eliminate pathogens present in the water.

Using a concentration of 25 mg/l is effective for achieving disinfection within a reasonable time frame, minimizing the risk of harmful microbial contamination while avoiding potential damage to the well components or the surrounding environment from excessively high chlorine levels. A shorter exposure time, coupled with a moderate concentration, balances effectiveness in disinfection while minimizing the impacts of chlorine residual in the system.

Longer exposure times or higher concentrations, as suggested in some other options, might be excessive for general purposes and can lead to complications or side effects, such as corrosion of pipes or undesirable taste and odor in the drinking water. Therefore, the specified exposure time and concentration are supported by best practices in water treatment to ensure safety and efficacy.