If chlorinated water shows a residual, what does this indicate?

When chlorinated water shows a residual, it indicates that chlorine is still present in the water after treatment, which suggests that the water treatment process has been effective in achieving disinfection. Chlorine is commonly used as a disinfectant to eliminate harmful pathogens in the water, and its residual presence signifies that there is still an active concentration of chlorine in the water.

This residual is crucial for ensuring that any remaining microorganisms are killed off as water moves through the distribution system, helping to prevent contamination that could occur after the initial treatment. Monitoring chlorine residuals is a standard practice in water treatment, as it provides a direct indication of the efficacy of disinfection and the ongoing protection of water quality up to the point of consumption.

The other options do not accurately reflect the implications of chlorine residual. While residual chlorine can be one factor in assessing safety, it does not directly indicate contamination or the need for further treatment on its own; instead, it points to the successful application of the treatment process.