Right, I have just found this: In the link given by Jared.
To treat potable water for storage, use liquid household chlorine bleach that contains 5 to 6 percent sodium hypochlorite. Almost any brand of bleach will do, the standard is 5 1/4% sodium hypochlorite and those labeled "Ultra" are typically 6%.
Avoid any bleach that is labeled as smelling of wildflowers, "rain clean" or with any other scent. You really don't want wildflower tasting water, trust me. You want plain old bleach, period. Bleach has a limited shelf life and for best results you should use fresh bleach no more that a few months old. Add bleach according to the following doses using a clean medicine dropper. You can usually get one for the asking or for a nominal price from your local pharmacy.
The base treatment is four drops of bleach per quart or liter of water or sixteen drops of bleach per gallon or four-liter container of water. If you're going to store large quantities, then just remember that 15 drops equals 1/4 teaspoon, so a teaspoonful equals 60 drops, enough to treat 3 3/4 gallons. A five gallon water can will take about 1 1/2 teaspoons of bleach.
Stir the water, cover, and allow to stand for 30 minutes. Uncap it and you ought to be able to smell chlorine. In the unlikely case that you don't, re-dose the water, stir, cover and let it stand another 30 minutes. Once done, seal or cap each container tightly. Be sure to label it clearly and permanently as potable water and the date you treated it.
Remember, water weighs over 8 pounds per gallon, 8.35 pounds to be exact, plus the weight of its container. Make sure any shelves you store it on are up to the task.
Properly treated water has been stored for periods of 2-5 years with no problems, especially when stored out of the light. Min d you, this water may taste very flat after long storage, but you can improve that a lot just by aerating it. Simply pour it from one container into another and back and forth a few times to improve the taste. This also tends to dissipate the residual chlorine, further improving the taste.
bushtucker