I got this from an article on Survivaltopics.com and thought it was interesting and might be of interest here.

Use Calcium Hypochlorite for Disinfect Water

A 1-pound pag of calcium hypochlorite in granular form will treat up to 10,000 gallons of drinking water

Calcium hypochlorite is one of the best chemical disinfectants for water, better than household bleach by far. It destroys a variety of disease causing organisms including bacteria, yeast, fungus, spores, and viruses.

Calcium Hypochlorite is widely available for use as swimming pool chlorine tablets or white powder that is much more stable than chlorine. This is often known as “pool shock”.
How to Disinfect Water Using Calcium Hypochlorite

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.

Another plus for using calcium hypochlorite to disinfect water for emergency use is that a little goes a very long way. A 1-pound pag of calcium hypochlorite in granular form typically costs only a few $US dollars and can be obtained in any swimming pool supply section of your hardware store or online. This amount will treat up to 10,000 gallons of drinking water, which is enough for a family of four for some six or seven years at a gallon per day per person!

Calcium hypochlorite will store for a long period of time and remain effective as a chemical drinking water treatment. So get rid of the household bleach and buy a can of Calcium hypochlorite for your disaster emergency water disinfection needs. It lasts far longer and treats far more water than the traditional chlorine bleach water disinfection treatment.