kill bacteria in the water
facilitate coagulation of organic particles
facilitate sedimentation
improve the taste of the water
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This is absolutely incorrect. Ca(OH)2 is only added to water in treatment in order to cause coagulation with an addition of potash alum,KAl(SO4)2 or Sodium aluminate(III),NaAlO2. This in turn sediment and is passed through a filter bed for filtration. The filtrate(i.e. liquid and not particles) is added to it iodine,fluorine and chlorine for specific purposes of which chlorine acts as a germicide. THANKS.

Google + Textbook... + my understanding of both sources:
Calcium hydroxide is added to reduce acidity and remove hardness of water. So it's main jobs: Maintain "safe" pH point or adjust pH, and water softening.
However, Calcium Hydroxide can also be used as a coagulant aid. It bonds with the particles, hence increasing the weight of the flics which then increases the speed with which it settles down the settling tank.
Also in the New School Chemistry Textbook, 2016 Edition, Pg 299, in the diagram for the treatment of water there, two tanks are foxed to the settling tank. One is alum and the other is Lime (Calcium Hydroxide). It only makes sense, then, that its job is also to facilitate coagulation..
Option B

Calcium hydroxide is added to town water supply in order to facilitate coagulation of organic particles. Coagulation is the process of clumping together of small particles into larger particles, which can then be removed from the water through sedimentation. The addition of calcium hydroxide raises the pH of the water, which helps the coagulation process by making the particles more attracted to each other. This helps to remove impurities from the water, making it cleaner and safer to drink. It does not directly kill bacteria in the water or improve the taste of the water.
So the correct answer is B

D to improve the taste of the water
Coagulation is done using Sodium Aluminate ( NaAlO2) and Potash Alum [KAl(SO4)2.12H2O]

6. Lime Treatment (Ca(OH) 2 ) - The addition of lime
and soda ash (Na 2CO 3) reduces the level of
calcium and magnesium in the water, and is
referred to as “lime softening”. The purpose of lime
softening is to remove hardness, and then clarify
the water and improve its taste.



