What reagent is commonly added to bottles for total coliform samples?

The addition of sodium thiosulfate to bottles for total coliform samples is essential for neutralizing chlorine or other disinfectants in the water sample. Chlorine is often used in water treatment processes to eliminate harmful microorganisms, but it can also kill coliform bacteria in the sample if present. This would lead to false-negative results in total coliform testing, as the disinfectant would inhibit the growth of these bacteria, which are indicators of water quality and potential contamination.

By including sodium thiosulfate in the collection bottles, analysts can ensure that any chlorine present is neutralized, allowing for an accurate assessment of the total coliform population in the sample. This step is crucial for obtaining reliable data that reflect the true microbiological content of the water being tested.