Certified in Public Health (CPH) Practice Exam

Which of the following disinfection methods is most commonly used in US drinking water supply systems?

1. Ozonation

2. Bromination

3. Chlorination

4. Ultraviolet irradiation

The correct answer is: Chlorination

Chlorination is the most commonly used disinfection method in drinking water supply systems in the United States due to its effectiveness and cost-efficiency. This process involves adding chlorine or chlorine compounds to water, which kills bacteria, viruses, and other pathogens, ensuring that the water is safe for consumption. Chlorine is favored because it not only disinfects water upon initial treatment, but it also provides a residual effect, continuing to eliminate any contaminants that might enter the water supply after treatment. The other methods listed, while effective in certain contexts, do not offer the same combination of broad-spectrum efficacy, residual protection, and regulatory acceptance as chlorination. Ozonation, for instance, is a powerful disinfectant but lacks a residual effect, meaning it does not protect the water as it travels through the distribution system. Bromination is less common for drinking water disinfection in the U.S. and is typically used in more specific applications, such as hot tubs and swimming pools. Ultraviolet irradiation is effective at inactivating microorganisms but also doesn't provide the necessary residual protection once the water leaves the treatment facility. Thus, chlorination remains the go-to method for ensuring safe drinking water across the U.S.