Using granular calcium hypochlorite to disinfect water is a two step process.
To make a stock of chlorine solution (do not drink this!) dissolve 1 heaping teaspoon (about one-quarter of an ounce) of high-test (78%) granular calcium hypochlorite for each two gallons (eight liters) of water. To disinfect water add one part of the chlorine solution to 100 parts water to be treated. Let the mixture sit for at least one-half hour before drinking. Be sure to obtain the dry granular calcium hypochlorite since once it is made into a liquid solution it will begin to degrade and eventually become useless as a disinfecting agent. This also means you should make your treated drinking water in small batches, for example enough for a few weeks at a time at most.