What is the purpose of using sodium-thiosulfate treated bottles for collecting chlorinated water samples?

Using sodium thiosulfate treated bottles for collecting chlorinated water samples serves the critical function of dechlorinating the sample. When water samples contain chlorine, it can adversely affect the accuracy of downstream analyses. Chlorine is a powerful disinfectant that can kill bacteria, including any that are being tested for in the water quality assessment. Therefore, if chlorine remains in the sample, it could lead to misleading results by artificially reducing the perceived levels of microbial content.

By adding sodium thiosulfate, which acts as a reducing agent, the chlorine is neutralized, effectively "dechlorinating" the water sample. This allows the organisms present in the sample to survive and be accurately quantified during testing. The goal is to ensure that the sample reflects its true microbial community and chemical composition, providing a more reliable basis for assessing water quality and safety.

This practice is essential in environmental health, especially in regulatory contexts where understanding the microbial quality of drinking water is crucial for public health.