Which chemical is most commonly used to disinfect public water supplies?

The primary chemical used to disinfect public water supplies is chlorine or chlorine compounds. This method has been widely adopted for several reasons: chlorine is effective at killing a broad range of pathogens, including bacteria, viruses, and some protozoa. It is relatively inexpensive and easy to apply at various scales, making it suitable for widespread use in municipal water systems.

Chlorination also provides a residual effect, meaning that chlorine remains in the water as it travels through the distribution system, offering ongoing protection against microbial contamination. This ensures that the water remains safe for consumption by the time it reaches the user.

Other disinfectants like bromine, iodine, and ozone may also be used in specific applications or regions, but they do not match chlorine's effectiveness and versatility in treating large public water supplies. For example, bromine is primarily used in swimming pools rather than large-scale water systems, and while ozone treatment is effective, it typically requires more complex equipment and does not provide long-term residual disinfection. Iodine is mostly used in emergency situations and for small-scale applications, such as water purification for personal use or in disaster scenarios. Therefore, chlorine or chlorine compounds stand out as the most prevalent choice for disinfecting public water supplies.