Personally, I avoid the use of all chlorines whenever possible. There are filters on my water system at home to eliminate it. I believe there are better ways of filtering or purifying water in an emergency.
But for the benefit of people who choose to use it. The following is the EPA guidelines on using calcium hypochlorite to disinfect water.
You can use granular calcium hypochlorite to disinfect water.
Add and dissolve one heaping teaspoon of high-test granular calcium hypochlorite (approximately ¼ ounce) for each two gallons of water, or 5 milliliters (approximately 7 grams) per 7.5 liters of water. The mixture will produce a stock chlorine solution of approximately 500 milligrams per liter, since the calcium hypochlorite has available chlorine equal to 70 percent of its weight. To disinfect water, add the chlorine solution in the ratio of one part of chlorine solution to each 100 parts of water to be treated. This is roughly equal to adding 1 pint (16 ounces) of stock chlorine to each 12.5 gallons of water or (approximately ½ liter to 50 liters of water) to be disinfected. To remove any objectionable chlorine odor, aerate the disinfected water by pouring it back and forth from one clean container to another.
The EPA guidelines do not discuss the storage requirements. You should be aware of the possible hazards of calcium hypochlorite. It’s a very powerful oxidant, and should be stored as such. Any contact with organic matter, can cause a violent chemical reaction.
Store the chemical in its original container in a cool, dry, well-ventilated place. Be sure the calcium hypochlorite container is tightly closed when not in use. Use only a clean, dry scoop (dedicated for this use) made of metal or plastic each time calcium hypochlorite is taken from the container. Add calcium hypochlorite only to water. A fire or explosion may result if calcium hypochlorite is mixed with other chemicals, including other pool chlorinating compounds, cyanuric acid, or pool treatment chemicals, contaminated with acids or brought into contact with any easily combustible materials such as oil, kerosene, gasoline, paint products and any other organic materials. Do not reuse empty calcium hypochlorite containers. They should be rinsed with water then destroyed when empty. Disposal of empty rinsed containers in garbage also is acceptable.
One word of warning DO NOT UNDER ANY CIRCUMSTANCES ALLOW THIS CHEMICAL TO MIX WITH ACID (or any solution with a pH<6) . The result will be free chlorine gas, the stuff that killed soldiers in WWI. You will die a horrible death within minutes from pulmonary edema. But since the water supply you will be working with usually has a pH of 7-8, this is not a problem.
When calcium hypochlorite comes in contact with ammonia or products containing ammonia it creates chloramines which is a toxic gas.
Read the labels on the containers and follow the instructions All handling and storage directions on the container should be followed to ensure accident free use of the chemical.