# The point at which the chlorine demand of water is met is termed:
A. Break point
B. Back wash
C. Loss of head
D. Chlorine demand
The correct answer is A. Break Point.
Chlorine demand of the water is the difference between the amount of chlorine added to the water and the amount of residual chlorine remaining at the end of a specific period of contact at a given temperature and pH of water.
The minimum recommended concentration of free chlorine is 0.5 mg per liter for one hour and it should be present for a contact period of at least one hour to kill bacteria and viruses.
The point at which chlorine demand of water is met is called break point. If further chlorine is added beyond the break point, free chlorine begins to appear in the water.
The sum of the chlorine demand of the water plus the free residual chlorine of 0.5 mg per liter constitutes the correct dose of chlorine to be applied.
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