What method is commonly used to keep municipally treated water free of bacteria?

Chlorination is a widely used method in municipal water treatment to ensure that water remains free of bacteria and other harmful microorganisms. The process involves adding chlorine or chlorine compounds to the water, which act as a disinfectant. Chlorine has strong oxidizing properties, making it effective at killing bacteria, viruses, and parasites that could pose health risks to consumers.

One of the main reasons chlorination is favored in municipal systems is its residual effect; the chlorine continues to provide disinfection even after the treatment process, thereby preventing microbial regrowth as the water travels through the distribution system. This ability to maintain a bactericidal environment is crucial in ensuring the safety of the water supplied to consumers.

The other methods mentioned, while they also play important roles in water treatment, are not as effective for long-term bacteriological control in distribution systems. For instance, boiling water is effective for immediate disinfection but is not practical for a municipal scale. Filtration can remove physical contaminants and some microorganisms but may not be as reliable for all pathogens unless combined with other disinfection methods. Ultraviolet light can effectively kill microorganisms, but it does not provide residual protection in the same way that chlorination does, making it less suitable as a standalone method in distribution systems.