Which of the following is not a method used for chlorine application?

The selection of post-chlorination of tap water as a method not used for chlorine application is grounded in the typical procedures for chlorine usage in water treatment processes. Generally, chlorination methods are categorized into stages based on when chlorine is introduced into the water treatment process: prechlorination, chlorination during the treatment process, and post-chlorination.

Prechlorination of inlet water refers to the application of chlorine to source water before any treatment processes take place, which helps control algae and bacteria. Injection prior to filtration refers to chlorinating water to eliminate pathogens before it undergoes filtration, ensuring cleaner water for the subsequent treatment stages.

Injection into finished water prior to storage aligns with common practices where chlorine is added to ensure that treated water remains disinfected during storage and distribution. This method is crucial for maintaining water quality as it reduces the risk of contamination after treatment.

However, the term "post-chlorination of tap water" is not typically employed because the term post-chlorination usually refers to the addition of chlorine after treatment and before distribution, rather than tap water itself, which is already at the consumption stage. Therefore, it stands out as the exception among the listed methods for chlorine application in the treatment processes.