BREAK POINT CHLORINATION. Ammonia compounds are introduced to pool water by bathers from urine contamination. When chlorine is added to water, it begins to react with these ammonia compounds and other organic matter and is gradually used up. Only the chlorine in combination with ammonia compounds is thus available for disinfection purposes and is spoken of as combined available chlorine. The reaction of chlorine with ammonia forms chloramines and some of these chloramines cause bather discomfort, eye irritation, and so called chlorine odour sometimes evident around a pool. When all chlorine in the water exists as chloramines it is known as margin chlorination and was in the past used as the main method of chlorination ammonium sulphate was added to the circulating water prior to filtration usually with the alum. The speed of disinfection by these chloramine compounds is very low. By the addition of sufficient chlorine all the chloramine can be destroyed in the water. However, when a pool is being used by bathers there will always be some chloramines in solution because of the continued introduction of impurities and the time necessary to destroy them. By the continuous addition of chlorine at the close of the swimming session the chloramine content will be reduced progressively. When all chloramines have been destroyed the residual or free chlorine and the total chlorine will be the same. When this point is reached Breakpoint Chlorination has been achieved. This is the best method of ensuring that water is free of disease producing organisms.
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