[Kartographer]

First bleach has a shelf life I prefer calcium hypochlorite.

http://readynutrition.com/resources/better-than-bleach-use-calcium-hypochlorite-to-disinfect-water_19062010/

Then there a whole host of contaminates that bleach won’t touch. You will need a good filter.

http://www.alpharubicon.com/kids/homemadeberkeydaire.htm

[PennsylvaniaMom]

68% Calcium hypo pool shock is easy to get—any pool store sells it. What you need to avoid is any shock that is “stabilized and/or conditioned.” For water purification make sure the shock does NOT contain cyanuric acid (that’s commonly referred to as “stabilizer.”)