The correct option is A Chlorination
Reservoir water passes through the following tanks for purification:
Reservoir → Sedimentation tank → Loading tank → Filtration tank → Chlorination tank → Supplied to home.
Sedimentation tank, loading tank and filtration tank are used to remove undissolved solid impurities from water.
After that, water is passed through the chlorination tank, where the bacteria are killed and water gets disinfected. Once water is purified, it becomes fit for drinking and is supplied to our homes.