What is the primary concern when chlorine is present in a water sample meant for bacteria testing?

The primary concern when chlorine is present in a water sample meant for bacteria testing is that it alters the sample composition. Chlorine is a powerful disinfectant that is commonly used in water treatment to kill harmful microbes, including bacteria. When chlorine is present in a water sample intended for microbiological testing, it can significantly affect the viability of bacteria within that sample.

If the chlorine concentration is high enough, it can inactivate or kill the bacteria that testers are attempting to detect. This means that the sample may not accurately reflect the true microbiological quality of the water, leading to false negative results. For valid testing results, it is essential that the water sample is free from chlorine and other disinfectants that can interfere with the analysis. Limiting or eliminating the presence of chlorine ensures that all bacteria present in the sample are still viable and can be accurately counted or identified during testing.