I found this:

“Add 16 drops of bleach, or 1/4 teaspoon, per gallon of water and stir.”

http://www.wisc.edu/foodsafety/consumer/fact_sheets/storingwater.htm

I think I tried 16 drops/gallon at first and when I opened the jug 6 months later the chlorine smell was very strong, so I cut back. You may want to do the same if your water is heavily chlorinated already. For 1.32 US gallons you'd add 21 drops.