Keep in mind the residual (for moderate and long term storage) biocidal effects of added chlorine will be dependant upon the availability of “free” chlorine and the bio-load (the concentration of organisms to be killed). Water, might contain large amounts of organic compounds (think of well water near farming operations), which may bind/tie up the “free” chlorine as chlorinated hydrocarbons (not real good for the body over time). If you are planning on storing and treating large amounts of water with chlorine, it might be wise to have the water tested for organic and chemical load/contamination or in a pinch, at least obtain a water test kit from an aquarium store and test the water yourself.

Pete