Florida Drinking Water Operator "B" Practice Test

Why is sodium thiosulfate added to sample bottles used for total coliform tests?

1. It enhances bacteria growth

2. It neutralizes the chlorine

3. It increases pH levels

4. It intensifies the color

The correct answer is: It neutralizes the chlorine

Sodium thiosulfate is added to sample bottles used for total coliform tests primarily to neutralize any residual chlorine present in the water sample. Chlorine is commonly used in water treatment processes to disinfect and kill harmful bacteria. However, if chlorinated water is tested directly, the chlorine can inhibit the growth of bacteria, leading to inaccurate results or false negatives in the total coliform tests. By adding sodium thiosulfate, any residual chlorine is effectively neutralized, providing a more accurate environment for the growth of coliform bacteria during the testing process. This ensures that the sample can truly reflect the presence or absence of coliform bacteria, which is crucial for assessing water quality and safety. Other options, such as enhancing bacteria growth or intensifying color, do not accurately describe the role of sodium thiosulfate in this context. Additionally, increasing pH levels is not relevant to the function of sodium thiosulfate in neutralizing chlorine. Thus, the correct reasoning revolves around its role in creating a conducive environment for accurate testing by eliminating chlorine interference.