Which of the following is NOT a common form of water contamination?

Chlorine is not a common form of water contamination. In fact, it is widely used as a disinfectant in water treatment processes to eliminate harmful microorganisms such as bacteria, viruses, and protozoa, which are all common forms of water contamination. The presence of bacteria, viruses, and protozoa in water can lead to serious health risks, as these pathogens can cause various waterborne diseases.

Chlorine, therefore, serves as a protective measure rather than a contaminant. Its role in water treatment is crucial for ensuring the safety and potability of drinking water, making it an essential component in maintaining public health standards. In contrast, the other options represent various microorganisms that can contaminate water sources and pose a threat to human health.