Chlorine Demand

When chlorine is added to water or applied to a surface, part of it reacts with organic soils, biofilm, ammonia and reducing agents rather than acting on target microorganisms. This consumed portion is the chlorine demand. Only chlorine remaining after this demand is met — the free available chlorine — is effective for disinfection.

Ignoring chlorine demand leads to under-dosed solutions that appear correct on paper but fail microbiologically. Heavily soiled surfaces or contaminated water sources may require pre-cleaning or a higher initial chlorine dose to compensate.

Considered in hospital cleaning protocols (clean before disinfect), water treatment, food-contact sanitisation, and outbreak response, where visibly soiled areas need pre-cleaning to ensure disinfectant efficacy.