What best describes chlorine residual in water treatment?

Chlorine residual refers to the chlorine concentration that remains in the water after it has undergone treatment processes. This measurement is crucial as it indicates the effectiveness of the disinfection process, ensuring that sufficient chlorine is present to kill or inactivate pathogens and provide ongoing protection against bacterial growth during the water's distribution. The presence of chlorine residual is also essential for confirming the water's safety, as it provides a buffer to counteract any potential contaminations that might occur before the water reaches the end user.

In contrast, the initial chlorine concentration before treatment pertains to the starting levels of chlorine before any interactions with contaminants, while the amount of chlorine that has reacted refers to the chlorine consumed during the disinfection process. The total amount of chlorine used encompasses the entirety of chlorine applied during treatment, but it does not specify how much remains after contaminants have been addressed. Hence, the residual measurement is critical to assess the ongoing disinfecting capability of the treated water.