I want to write a bit more about water purification. Here are some guidelines on the use of calcium to treat water. http://bit.ly/UgeSXC Again I want to remind you of the dangers of storing calcium hypochlorite. Read the hazards on the labels and pay attention to them. It is a strong oxidizer and I have seen it cause fires and explosive reactions.
Another chemical that I occasionally hear about for water treatment is hydrogen peroxide. It is a chemical compound with many uses. I have to admit to being a little confused by this chemical. I have found a lot of conflicting information on the subject of storing it and using it to treat water. It is often used in large municipal treatment plants, but in 35% solution. At this strength, inhaling hydrogen peroxide can cause lung problems and the effect of chronic exposure to hydrogen peroxide is not yet entirely known.
Hydrogen peroxide has a shelve life, and it needs to be kept in a dark bottle that blocks out sunlight. Potency could be an issue if it has been stored for a long period. The shelve life seems to be largely dependent on temperature and how pure the solution is. I am not sure how you would determine this under emergency conditions.
The hydrogen peroxide that we commonly buy at the drug store is a 3% solution. It is my understanding that 7% is the standard water treatment strength. In the large treatment plants, they use 35% solutions, but determine its effectiveness by measuring parts per million in the water. I have not found a reliable method of determining how much hydrogen peroxide to use to treat your water. I have found claims that it will work in various strengths, but nothing that I trust (including up to 1 pint of 3% per gallon of water).
At this time, I am recommending that you do not use this method as your primary method of purifying water, but it is something you may be able to try in a real emergency. My mind is still open on the subject of using hydrogen peroxide, so if you have additional information I would like to see it and share it with others.