"Have bottles & bleach, will store water.."

I was about to search the forum about that kind of info : how much bleach to add per gallon of water, because I have now a few 5liters bottles at hand (that's 1.32 US gallon bottles).
So, I should use 1/5th of tea spoon.... let's see...
Anyway I don't have tea spoons, only coffee spoons.... or rather dessert spoons...
Not really scientific measurements..

May be I should search the forums (IRC, there have been many threads on that subject) and try to find a measure in drops ??