What chemical is likely needed for each routine sampling round?

In water quality testing, particularly in Legionella management, sodium thiosulfate is often utilized during routine sampling rounds. The primary purpose of sodium thiosulfate is to neutralize chlorine or chloramines present in the water sample. Chlorine can be an effective disinfectant, but it can also affect the accuracy of microbiological tests for organisms like Legionella. By adding sodium thiosulfate to the sample, any residual chlorine is neutralized, allowing for a more accurate assessment of the cultured organisms. This step is vital to ensure that the test results truly reflect the Legionella presence in the sample without being influenced by the sanitizer levels that may otherwise inhibit growth during testing.

The other choices provide different functionalities that are not suited for routine sampling. For example, chlorine dioxide is a disinfectant that is used for water treatment but would similarly interfere with testing if residuals remained in the sample. Calcium hypochlorite is also a disinfectant, primarily used for pool and drinking water treatment, and would present the same inhibitory challenge during sampling. Potassium bromide is another disinfectant, but it does not serve the specific function of neutralizing chlorine for accurate microbiological testing. Thus, sodium thiosulfate is the appropriate chemical for ensuring accurate