What happens to the residual chlorine after the demand is met?

When chlorine is added to water for disinfection purposes, it first reacts with any organic or inorganic material in the water, which is known as meeting the chlorine demand. After this is accomplished, any remaining chlorine that has not been consumed by these reactions persists in the water. This remaining chlorine is referred to as "residual chlorine." It plays a crucial role in maintaining ongoing disinfection as water moves through the distribution system.

The presence of residual chlorine is vital for ensuring the microbiological safety of the drinking water as it continues to inhibit the growth of pathogens until it reaches the consumer. Thus, the fact that residual chlorine remains in the system post-demand is key to effective water treatment and public health protection.

Other answers reflect misunderstandings about the properties of chlorine in water. Residual chlorine is not rendered useless; it does not disappear entirely (as total elimination would imply that no residual chlorine remains for further disinfection), nor is it stored in tanks as a separate entity after being added to the water.