All of the following are true about break point chlorination, except –

Principles of chlorination                                                                                Water should be clear and free from turbidity. Turbidity impedes efficient chlorination. The chlorine demand of the water should be estimated. It is the amount of chlorine that is needed to destroy bacteria and to oxidize all the organic matter and ammoniacal substances present in water. Chlorine demand of water is the difference between the amount of chlorine added to the water and the amount of residual chlorine remaining at the end of specific period of contact (usually 60 minutes) at a given temperature and pH of the water. The point at which the chlorine demand of the water is met is called break point chlorination. If further chlorine is added beyond break point, free chlorine begins to appear in water. The presence of free residual chlorine for a contact period of at least one hour is essential to kill bacteria and virus. The minimum recommended concentration of free chlorine is 0.5mg/i for one hour. This free residual chlorine provides margin of safety against subsequent microbial contamination. The sum of the chlorine demand of the specific water plus the free residual chlorine of .5 mg/L constitutes the correct does of chlorine to be applied. It is worth noting here that recommended residual chlorine level for drinking water is 0.5 mg/ litre, while for swimming pool sanitation it is 1.0 mg/ litre and for water bodies & post disaster it is 0.7 mg/litre