Florida Drinking Water Operator "B" Practice Test

If using free chlorine, what is the minimum required free chlorine residual needed in the distribution system?

1. 0.2 mg/l

2. 0.5 mg/l

3. 1.0 mg/l

4. 1.5 mg/l

The correct answer is: 0.5 mg/l

The minimum required free chlorine residual in the distribution system is established to ensure that there is enough disinfectant available to effectively kill pathogens and maintain water quality as it travels through the distribution network. A free chlorine residual of 0.5 mg/l is recognized as the minimum threshold needed to provide adequate disinfection and ensure safety for consumers. This level helps to maintain a sufficient concentration of chlorine to act against bacteria and other harmful microorganisms while also minimizing the risk of waterborne diseases. Residual levels lower than this minimum may not provide effective disinfection throughout the distribution system, especially in areas that may be more susceptible to contamination. Higher levels of chlorine residual might be effective in disinfection but could lead to other issues such as taste and odor problems, or even the formation of potentially harmful by-products, making 0.5 mg/l a balanced choice. Other options present higher concentrations, which, while they may contribute to disinfection, are not necessary for a minimal effective concentration.