What indicates that successful disinfection has occurred?

A negative coliform result is a crucial indicator of successful disinfection in water distribution systems. Coliform bacteria, including Escherichia coli (E. coli), are used as indicators of fecal contamination and the overall cleanliness of water. The presence of these bacteria suggests that water may be contaminated with pathogens, making it unsafe for consumption. Therefore, a negative result indicates that disinfection processes, such as chlorination, have effectively eliminated coliform bacteria, signifying that the water is more likely to be safe for public use.

While a high chlorine residual (which suggests the presence of chlorine not yet reacted with contaminants) can indicate effective disinfection has occurred, it does not definitively confirm the absence of harmful microorganisms. Chlorine can dissipate over time and may not fully reflect the condition of the water if tested later after chlorine levels drop. Other options, like a positive coliform result, would indicate that disinfection was not successful, while normal pressure in the tank relates to operational functionality rather than disinfection efficacy. Therefore, the presence of a negative coliform result clearly signifies that the disinfection process has accomplished its vital goal of producing safe drinking water.