How can we use bleaching powder to purify water?


We are facing a lot of problems of drinking water in our company guest house. we dont have any RO unit. We are directly using well water for drinking purpose. We are planning to use bleaching powder for purification. Is there any food grade powder available in the market? Can we use this directly in the storage tank? Are there any prescribed dosages to be used? Kindly guide us. Also if there are any alternate chemicals that can be used please suggest.  

Thanks & Regards

Pandian B

NSL Sugars Ltd , Beed , Maharastra