Pool shock.
I searched here quickly but could not find the specific posts (the "be prepared" thread and others probably have great info on mixture but too long for me to read at the moment).
So, FWIW here is one link from outside...hope it helps.
"Add one heaping teaspoon of granular calcium hypochlorite to two gallons of water, or 5 ml. to 7.5 l. of water. This mixture produces a solution similar to bleach.
Use one part of this solution to 100 parts of water to be treated. Allow the mixture to sit for at least 30 minutes before drinking. If the smell of chlorine is too strong, pour the pure water from one container into another several times to allow the chlorine to dissipate.
WARNINGS: Do not breathe the toxic fumes from the pool shock. Store away from anything flammable, including paper, gasoline, oil, oily rags, and paint solvent. Additionally, do not store near any type of ignition sources, such as lawn mowers, generators, etc."
http://thesurvivalmom.com/wp-content...r-Purifier.pdf